Relay type catalyst for lithium-sulfur battery as well as preparation method and application of relay type catalyst

Abstract

The invention relates to the technical field of battery material preparation, in particular to a lithium-sulfur battery relay type catalyst and a preparation method and application thereof.The preparation method comprises the steps that Bi (NO3) 3 and an FAU type molecular sieve are mixed and dispersed in an organic mixed solvent, and a mixed solution is formed; carrying out hydrothermal treatment on the mixed solution to obtain a solid product; and calcining the solid product to realize preparation of the relay type catalyst for the lithium-sulfur battery, finally forming a structure of compounding the FAU type molecular sieve on the Bi2O3 nanosheet, and effectively capturing and guiding polysulfide to transfer to a metal oxide interface by utilizing a rich microporous structure of the FAU type molecular sieve during catalysis, so that the catalytic performance of the lithium-sulfur battery is improved. High-activity sites on the surface of Bi2O3 catalyze polysulfide to be rapidly converted into LiS, meanwhile, product desorption is promoted, through the relay effect of the FAU type molecular sieve and Bi2O3, rapid conversion is promoted, reaction kinetics is enhanced, the shuttle effect is inhibited, and the reaction efficiency is improved. The problems of low conversion kinetics and short cycle life of the battery caused by a polysulfide shuttle effect of the lithium-sulfur battery in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the field of battery material preparation, and in particular to a relay catalyst for lithium-sulfur batteries, a preparation method and an application thereof, and more particularly to a relay catalyst for lithium-sulfur batteries composed of FAU-type zeolite composite metal oxide, a preparation method and an application thereof. Background Art

[0002] The lithium-sulfur battery (Lithium-sulfur battery, Li-S battery) is a type of lithium battery, which is unique in that it uses sulfur as the positive electrode material of the battery, while metallic lithium is used as the negative electrode. The lithium-sulfur battery has attracted wide attention due to its high specific capacity of 1675 mAh g -1 and a theoretical energy density of up to 2600 Wh kg -1 , abundant sulfur resources and low price.

[0003] However, the practical application of lithium-sulfur batteries faces some inherent challenges. First, the inherently low electrical conductivity of the active material sulfur (5×10 -30 S cm -1 ), and its discharge product lithium sulfide (Li2S) severely limits the reaction kinetics. Secondly, during the discharge process, the breaking of the S-S bond generates polysulfide (LiPS), which is highly soluble in the electrolyte, resulting in a serious "shuttle effect". As the reaction proceeds, the dissolved LiPS species migrate towards the lithium anode under the concentration gradient, leading to the loss of active material and serious parasitic side reactions. In addition, the slow conversion kinetics of polysulfide to lithium sulfide hinders the performance, resulting in severe capacity attenuation and cycling instability. These problems together limit the commercialization of lithium-sulfur batteries. Therefore, the polysulfide shuttle effect is the main reason for the capacity attenuation and performance instability of lithium-sulfur batteries. Summary of the Invention

[0004] Aiming at the problems of low conversion kinetics and short battery cycle life caused by the polysulfide shuttle effect in lithium-sulfur batteries in the prior art, the present invention provides a relay catalyst for lithium-sulfur batteries, a preparation method and an application thereof.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a preparation method for a relay catalyst for lithium-sulfur batteries, including: Mixing and dispersing Bi(NO3)3 and FAU-type zeolite in an organic mixed solvent to form a mixed solution; Subjecting the mixed solution to hydrothermal treatment to obtain a solid product; Calcining the solid product to obtain a relay catalyst for lithium-sulfur batteries.

[0006] Optionally, the mass ratio of Bi(NO3)3 to the FAU zeolite is (9.7 to 38.8):1.

[0007] Optionally, the mechanical mixed solvent is a mixed solution of ethanol and ethylene glycol.

[0008] Optionally, the volume ratio of ethanol to ethylene glycol is 2:1.

[0009] Optionally, the conditions for hydrothermal treatment are 170°C to 190°C, with heat preservation for 8 to 12 hours.

[0010] Optionally, the calcination conditions are 500°C to 600°C, with heat preservation for 1 to 3 hours.

[0011] A relay catalyst for lithium-sulfur batteries is prepared by the above method.

[0012] The application of the relay catalyst for lithium-sulfur batteries as described above in the preparation of a lithium-sulfur battery separator includes: Mixing and dispersing the relay catalyst for lithium-sulfur batteries, acetylene black, and a binder in an NMP solvent to form a slurry; Coating the slurry on a PP separator and drying to obtain a lithium-sulfur battery separator.

[0013] Optionally, the mass ratio of the relay catalyst for lithium-sulfur batteries, acetylene black, and the binder is 2:7:1; the thickness of the lithium-sulfur battery separator is 13 to 16 μm.

[0014] A lithium-sulfur battery includes the above-mentioned lithium-sulfur battery separator.

[0015] Compared with the prior art, the present invention has the following beneficial effects: A relay catalyst for lithium-sulfur batteries according to the present invention. In this method, metal nitrate and FAU-type molecular sieve are mixed and dispersed in an organic mixed solvent to form a mixed solution; the mixed solution is hydrothermally treated to obtain a solid product; the solid product is calcined to prepare the relay catalyst for lithium-sulfur batteries. Through the hydrothermal reaction, metal nitrate and FAU-type molecular sieve are combined by hydrogen bonds or chemical bonds to form a stable composite structure. Through calcination, metal nitrate is decomposed into highly active metal oxides, forming a composite of metal oxides and FAU-type molecular sieve. Finally, a structure in which FAU-type molecular sieve is composited on metal oxide nanosheets is formed. During catalysis, by utilizing the rich microporous structure of FAU-type molecular sieve, polysulfides are effectively captured and guided to the interface of metal oxides. The highly active sites on the surface of metal oxides catalyze the rapid conversion of polysulfides into Li2S, and at the same time promote the desorption of products, avoiding the blockage of active sites. Through the relay effect of FAU-type molecular sieve and metal oxides, not only the rapid conversion is promoted and the reaction kinetics is enhanced, but also the "shuttle effect" is inhibited. Integrating this relay catalyst for lithium-sulfur batteries onto a commercial separator can not only improve the electrochemical performance, but also has excellent flame retardant properties, providing a new way to promote the practical application of lithium-sulfur battery technology.

[0016] The present invention provides a relay catalyst for lithium-sulfur batteries, which is prepared by the above method. This relay catalyst for lithium-sulfur batteries is a structure in which metal oxide nanosheets support nanoscale FAU-type molecular sieve. This structure can capture sulfides to the active centers of metal oxide nanosheets through the FAU-type molecular sieve structure. The metal oxide nanosheets catalyze the rapid conversion of polysulfides into Li2S. At the same time, the thin layer structure of the metal oxide nanosheets undergoes slight deformation during charge and discharge, and the generated mechanical stress can accelerate the desorption of Li2S products, avoid the passivation of active sites, promote the desorption of products, quickly complete the "adsorption-conversion-desorption" closed loop, and smoothly achieve relay catalysis. It has high catalytic efficiency and good reaction kinetics, and realizes the efficient dynamic management of polysulfides from adsorption to conversion.

[0017] Application of the relay catalyst for lithium-sulfur batteries as described above in the preparation of lithium-sulfur battery separators. The modified separator loaded with this relay catalyst for lithium-sulfur batteries has not only excellent mechanical properties but also remarkable flame retardant properties when applied to the lithium-sulfur battery separator.

[0018] A lithium-sulfur battery includes the above lithium-sulfur battery separator, and this lithium-sulfur battery has higher Coulomb efficiency, better electrical performance and longer cycle service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic flow chart of the preparation method of a relay catalyst for lithium-sulfur batteries according to the present invention.

[0020] Figure 2 SEM and elemental distribution maps of the relay catalyst for the lithium-sulfur battery prepared in Example 1 of the present invention; among them, a is the SEM image of Bi2O3 nanosheets; b is the SEM image of FAU-type zeolite; c is the SEM image of the relay catalyst for the lithium-sulfur battery prepared in Example 1; d is the EDS elemental distribution map of the relay catalyst for the lithium-sulfur battery prepared in Example 1.

[0021] Figure 3 Comparison diagrams of the bending of the separator and the wettability of the electrolyte of the lithium-sulfur battery prepared by using the relay catalyst for the lithium-sulfur battery of the present invention; among them, a is the bending test diagram of the mechanical properties, and b is the test result diagram of the electrolytic infiltration wettability.

[0022] Figure 4 Electrochemical performance test diagrams of the lithium-sulfur battery prepared by using the relay catalyst for the lithium-sulfur battery of the present invention; among them, a is the cycle stability of the lithium-sulfur battery with different separators at 0.2C; b is the charge-discharge curve diagram of the separator prepared by the catalyst of the present invention at 0.2C under different cycle numbers. Detailed implementation manners

[0023] To enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0024] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not in any way limit the scope of the present invention, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0025] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0026] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar terms cover the meanings of "consisting of" and "mainly consisting of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0027] In this document, for the sake of brevity of description, not all possible combinations of all the technical features in each implementation or embodiment are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation or embodiment can be combined arbitrarily, and all possible combinations should be considered to be within the scope described in this specification.

[0028] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0029] Conventional instruments and equipment in the art are used in the following embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0030] The present invention will be further described in detail below in conjunction with specific embodiments. The following is an explanation rather than a limitation of the present invention.

[0031] Lithium-sulfur (Li-S) batteries have become promising energy storage devices due to their high energy density. However, the slow kinetics of lithium polysulfide (LiPSs) conversion leads to rapid capacity decay, limiting their practical applications. Since the catalytic process in lithium-sulfur batteries includes three processes, the first step is the diffusion and adsorption of polysulfides to the catalyst active sites; the second step is the catalytic conversion of polysulfides by the catalyst; the third step is the desorption of lithium sulfide, the catalytic product. In each of the three stages of catalysis, each step is crucial, and the catalytic efficiency is affected by each step. Although the prior art has disclosed a variety of catalysts to solve this problem, most existing Li-S battery catalysts only focus on the catalytic conversion step, leaving much room for improvement in the existing catalytic kinetics. Therefore, a catalyst that can further enhance the catalytic reaction kinetics throughout the catalytic process is needed to improve the electrochemical performance of lithium-sulfur batteries. Herein, we propose a preparation method for a relay catalyst for lithium-sulfur batteries to accelerate the sulfur reduction conversion process of lithium-sulfur batteries throughout the catalysis. We synthesized a relay catalyst with a nano-FAU zeolite and Bi2O3 lamellar structure. By designing the components and structure of the catalyst, different stages of the catalytic process were optimized. Utilizing the rich microporous structure of FAU zeolite, polysulfides were effectively captured and guided to the Bi2O3 interface, realizing the optimization of the first step of polysulfide catalysis. During the catalytic process of the second step, with the rich active sites on the Bi2O3 interface, the Bi2O3 catalytic center promoted rapid conversion and enhanced the reaction kinetics. Under mechanical action, the desorption process after catalysis was promoted through the setting of this special structure, realizing the optimization of the third step of the catalytic process. By relaying the three steps of polysulfide conversion, rapid conversion kinetics were achieved, thereby improving the battery's electrochemical performance. In addition, integrating this relay catalyst for lithium-sulfur batteries onto the separator can not only improve the electrochemical performance but also has excellent flame retardant properties. The specific scheme is described as follows: The present invention discloses a preparation method for a relay catalyst for lithium-sulfur batteries, referring to Figure 1 , including: S11: Mix and disperse metal nitrates and FAU zeolite in an organic mixed solvent to form a mixed solution, specifically: Mix and disperse Bi(NO3)3 and FAU zeolite in an organic mixed solvent at a mass ratio of (9.7 - 38.8):1, ultrasonically treat and stir to form a mixed solution; the organic mixed solvent is a mixed solution of ethanol and ethylene glycol with a volume ratio of 2:1; preferably, the FAU zeolite is X-type zeolite and / or Y-type zeolite; S12: Hydrothermally treat the mixed solution to obtain a solid product, specifically: Transfer the mixed solution to a high-pressure reaction vessel lined with polytetrafluoroethylene, heat it to 170 °C - 190 °C, keep it warm for 8 - 12 h, then cool it to room temperature, centrifuge it, and wash it alternately with deionized water and ethanol, and dry it to obtain a solid product; S13: Calcinate the solid product to obtain a relay catalyst for lithium-sulfur batteries, specifically: Transfer the solid product to a covered corundum crucible, place it in a muffle furnace, heat it to 500 °C - 600 °C at a rate of 5 °C / min - 10 °C / min, and keep it warm for 1 - 3 h to obtain a relay catalyst for lithium-sulfur batteries.

[0032] Example 1 At room temperature, disperse Bi(NO3)3 (0.97 g, 0.002 mol) and FAU-type zeolite (25 mg) in a mixed solution of 34 mL of ethanol and 17 mL of ethylene glycol, ultrasonically treat it for 5 min, and stir it for 30 min to obtain a mixed solution. Transfer the obtained mixed solution to a high-pressure reaction vessel lined with polytetrafluoroethylene, heat it to 180 °C and keep it for 10 h, then cool it to room temperature, centrifuge it, wash it alternately with deionized water and ethanol, and dry it at 60 °C for 8 h to obtain a solid product. Finally, transfer the dried solid product to a covered corundum crucible, place it in a muffle furnace, and calcine it at 550 °C for 2 h (heating rate is 10 °C / min) to obtain a relay catalyst for lithium-sulfur batteries.

[0033] See Figure 2 , conduct SEM tests and elemental analysis on the prepared relay catalyst for lithium-sulfur batteries. The results show that during the formation of Bi2O3, the FAU-type zeolite is dispersed and introduced into the Bi2O3 nanosheet structure to form a FAU-Bi2O3 composite structure. The morphology of this composite structure retains the flower-like structure formed by the stacked layers of Bi2O3, and smaller FAU-type zeolite particles are evenly embedded in this layered structure. This unique structure promotes the adsorption of nano-polysulfides by FAU zeolite in lithium-sulfur batteries and promotes the catalytic conversion of nano-polysulfides on the surface of Bi2O3.

[0034] Example 2 At room temperature, Bi(NO3)3 (0.97 g, 0.002 mol) and FAU zeolite (25 mg) were dissolved in a mixed solution of 34 mL of ethanol and 17 mL of ethylene glycol. The mixture was ultrasonically treated for 5 min, stirred for 30 min, and thoroughly mixed to ensure complete dissolution. The resulting mixed solution was transferred to a high-pressure reaction vessel lined with polytetrafluoroethylene, heated to 180 °C and maintained for 10 h, then cooled to room temperature, centrifuged, washed alternately with deionized water and ethanol, and dried at 60 °C for 8 h to obtain a solid product. Finally, the dried solid product was transferred to a covered corundum crucible, placed in a muffle furnace, and calcined at 550 °C for 2 h (heating rate: 10 °C / min) to obtain a relay catalyst for lithium-sulfur batteries, denoted as FAU-Bi2O3-25.

[0035] Example 3 At room temperature, Bi(NO3)3 (0.97 g, 0.002 mol) and FAU zeolite (50 mg) were dissolved in a mixed solution of 34 mL of ethanol and 17 mL of ethylene glycol, ultrasonically treated for 5 min, and stirred for 30 min to obtain a mixed solution. The mixed solution was transferred to a high-pressure reaction vessel lined with polytetrafluoroethylene, heated to 180 °C and maintained for 10 h, then cooled to room temperature, centrifuged, washed alternately with deionized water and ethanol, and dried at 60 °C for 8 h to obtain a solid product. The dried solid product was transferred to a covered corundum crucible, placed in a muffle furnace, and calcined at 550 °C for 2 h (heating rate: 10 °C / min) to obtain a relay catalyst for lithium-sulfur batteries, denoted as FAU-Bi2O3-50.

[0036] Example 4 At room temperature, Bi(NO3)3 (0.97 g, 0.002 mol) and FAU zeolite (100 mg) were dissolved in a mixed solution of 34 mL of ethanol and 17 mL of ethylene glycol, ultrasonically treated for 5 min, and stirred for 30 min to obtain a mixed solution. The resulting mixed solution was transferred to a high-pressure reaction vessel lined with polytetrafluoroethylene, heated to 180 °C and maintained for 10 h, then cooled to room temperature, centrifuged, washed alternately with deionized water and ethanol, and dried at 60 °C for 8 h to obtain a solid product. Finally, the dried solid product was transferred to a covered corundum crucible, placed in a muffle furnace, and calcined at 550 °C for 2 h (heating rate: 10 °C / min) to obtain a relay catalyst for lithium-sulfur batteries, denoted as FAU-Bi2O3-100.

[0037] The application of the relay catalyst for lithium-sulfur batteries as described above in the preparation of a lithium-sulfur battery separator includes: S21: Mix and disperse the relay catalyst for lithium-sulfur battery, acetylene black, and binder in N-Methylpyrrolidone (NMP) solvent to form a slurry, specifically: Mix the relay catalyst for lithium-sulfur battery, acetylene black, and binder in a mass ratio of 2:7:1 in NMP solvent to form a slurry, and the binder is Polyvinylidene Fluoride (PVDF).

[0038] S22: Coat the slurry on a Polypropylene (PP) separator, and dry it to obtain a lithium-sulfur battery separator, specifically: Apply the slurry evenly on the surface of the PP separator, and dry it under vacuum conditions to obtain a lithium-sulfur battery separator. Preferably, the PP separator is Celgard 2500 PP separator.

[0039] Example 5 Mix FAU-Bi2O3-25, acetylene black, and binder PVDF in a mass ratio of 2:7:1, and then stir in NMP solvent to prepare a slurry for coating the separator. Then place it in NMP solvent and stir to prepare a slurry for coating the separator. Use a scraper to evenly apply the obtained slurry on the surface of a commercial Celgard 2500 PP separator, transfer it to a vacuum furnace, and dry it at 60 °C for 12 h to obtain a lithium-sulfur battery separator. Cut the lithium-sulfur battery separator into discs with a diameter of 19 mm, and the coating thickness on the lithium-sulfur battery separator is 15 μm.

[0040] Example 6 Mix FAU-Bi2O3-50, acetylene black, and binder PVDF in a mass ratio of 2:7:1, and then stir in NMP solvent to prepare a slurry for coating the separator. Then place it in NMP solvent and stir to prepare a slurry for coating the separator. Use a scraper to evenly apply the obtained slurry on the surface of a commercial Celgard 2500 PP separator, transfer it to a vacuum furnace, and dry it at 60 °C for 12 h to obtain a lithium-sulfur battery separator. Cut the lithium-sulfur battery separator into discs with a diameter of 19 mm, and the coating thickness on the lithium-sulfur battery separator is 15 μm.

[0041] See Figure 3 , conduct a bending test and an electrolyte wettability test on the prepared lithium-sulfur battery separator. It can be seen that the lithium-sulfur battery separator has good contact with the electrolyte, which can ensure the rapid transfer of lithium ions during the reaction of the lithium-sulfur battery. The functional separator coating loaded with FAU-Bi2O3 exhibits excellent mechanical properties and returns to its original state after bending.

[0042] Example 7 FAU-Bi2O3-100, acetylene black, and binder PVDF were mixed at a mass ratio of 2:7:1, and then stirred in NMP solvent to prepare a slurry for coating the separator. Then it was placed in NMP solvent and stirred to prepare a slurry for coating the separator. The resulting slurry was uniformly applied to the surface of a commercial Celgard 2500 PP separator using a doctor blade, transferred to a vacuum furnace, and dried at 60 °C for 12 h to obtain a lithium-sulfur battery separator. The lithium-sulfur battery separator was cut into discs with a diameter of 19 mm, and the coating thickness on the lithium-sulfur battery separator was 15 μm.

[0043] The present invention also provides a lithium-sulfur battery, including the above-mentioned lithium-sulfur battery separator.

[0044] Example 8 The present invention provides a lithium-sulfur battery, including a positive electrode, a negative electrode, an electrolyte, and the lithium-sulfur battery separator described in Example 5.

[0045] The positive electrode is composed of carbon nanotubes, acetylene black, a binder, and sublimed sulfur. Among them, by mass percentage: carbon nanotubes are 20% - 30%, sublimed sulfur is 50% - 70%, acetylene black is 5% - 15%, the binder is polyvinylidene fluoride, and the binder content is 5% - 15%; Carbon nanotubes, acetylene black, and binder PVDF were mixed and ground, N-methyl-2-pyrrolidone (NMP) was added to make a slurry, and it was coated on carbon-coated aluminum foil and dried at 60 °C to obtain a lithium-sulfur positive electrode.

[0046] The negative electrode is metallic lithium.

[0047] The lithium-sulfur battery separator is the lithium-sulfur battery separator prepared in any one of Examples 5 - 7.

[0048] The positive electrode, negative electrode, electrolyte, and separator were assembled into a button battery for electrical performance testing.

[0049] Example 9 The present invention provides a lithium-sulfur battery, including a positive electrode, a negative electrode, an electrolyte, and the lithium-sulfur battery separator described in Example 6.

[0050] The positive electrode is composed of carbon nanotubes, acetylene black, a binder, and sublimed sulfur. Among them, by mass percentage: carbon nanotubes are 20%, sublimed sulfur is 70%, acetylene black is 5%, the binder is polyvinylidene fluoride, and the binder content is 5%; Carbon nanotubes, acetylene black, and binder PVDF were mixed and ground, N-methyl-2-pyrrolidone (NMP) was added to make a slurry, and it was coated on carbon-coated aluminum foil and dried at 60 °C to obtain a lithium-sulfur positive electrode.

[0051] The negative electrode is metallic lithium.

[0052] The positive electrode, negative electrode, electrolyte and separator are assembled into a button cell for electrical performance testing.

[0053] Comparative Example 1 The present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, an electrolyte and the lithium-sulfur battery separator described in Example 6.

[0054] The positive electrode is composed of a composite of carbon nanotubes, acetylene black, a binder and sublimed sulfur. Among them, by mass percentage: carbon nanotubes are 20%, sublimed sulfur is 70%, acetylene black is 5%, the binder is polyvinylidene fluoride, and the binder content is 5%; The carbon nanotubes, acetylene black and binder PVDF are mixed and ground, N-methyl-2-pyrrolidone (NMP) is added to make a slurry, which is then coated on carbon-coated aluminum foil and dried at 60 °C to obtain a lithium-sulfur positive electrode.

[0055] The negative electrode is metallic lithium.

[0056] Bi2O3, acetylene black and binder PVDF are mixed in a mass ratio of 2:7:1, and then stirred in an NMP solvent to prepare a slurry for coating the separator. Then it is placed in an NMP solvent and stirred to prepare a slurry for coating the separator. The obtained slurry is evenly applied to the surface of a commercial Celgard 2500 PP separator using a doctor blade, transferred to a vacuum furnace, and dried at 60 °C for 12 h to obtain a lithium-sulfur battery separator. The lithium-sulfur battery separator is cut into a disc with a diameter of 19 mm, and the coating thickness on the lithium-sulfur battery separator is 15 μm.

[0057] The positive electrode, negative electrode, electrolyte and separator are assembled into a button cell for electrical performance testing.

[0058] Comparative Example 2 The present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, an electrolyte and the lithium-sulfur battery separator described in Example 6.

[0059] The positive electrode is composed of a composite of carbon nanotubes, acetylene black, a binder and sublimed sulfur. Among them, by mass percentage: carbon nanotubes are 20%, sublimed sulfur is 70%, acetylene black is 5%, the binder is polyvinylidene fluoride, and the binder content is 5%; The carbon nanotubes, acetylene black and binder PVDF are mixed and ground, N-methyl-2-pyrrolidone (NMP) is added to make a slurry, which is then coated on carbon-coated aluminum foil and dried at 60 °C to obtain a lithium-sulfur positive electrode.

[0060] The negative electrode is metallic lithium.

[0061] The FAU zeolite, acetylene black, and binder PVDF are mixed at a mass ratio of 2:7:1, and then stirred in an NMP solvent to prepare a slurry for coating the separator. Then it is placed in an NMP solvent and stirred to prepare a slurry for coating the separator. The resulting slurry is evenly applied to the surface of a commercial Celgard 2500 PP separator using a doctor blade, transferred to a vacuum furnace, and dried at 60 °C for 12 h to obtain a lithium-sulfur battery separator. The lithium-sulfur battery separator is cut into circular pieces with a diameter of 19 mm, and the coating thickness on the lithium-sulfur battery separator is 15 μm.

[0062] The positive electrode, negative electrode, electrolyte, and separator are assembled into a button battery for electrical performance testing.

[0063] Reference Figure 4 , the electrochemical performance tests were carried out on Example 9, Comparative Examples 1 and 2, and the blank PP separator. It was found that the first discharge of the lithium-sulfur battery with the FAU-Bi2O3 lithium-sulfur battery relay-type catalyst separator was 1500 mAh g -1 , and still had a high specific capacity of 846.81 mAh g after 100 cycles at 0.2 C -1 , while the separators with PP, FAU zeolite, and Bi2O3 catalysts had specific capacities of 485.9, 692.1, and 696 mAh g -1 . In addition, the charge-discharge curves of the lithium-sulfur battery with the FAU-Bi2O3 catalyst separator at the 1st, 10th, 20th, 30th, 40th, and 50th cycles also showed its typical lithium-sulfur discharge process and low capacity decay rate. It should be noted that in the figure, PP represents the lithium-sulfur battery with a pure PP separator combination, FAU represents the lithium-sulfur battery prepared in Comparative Example 2, Bi2O3 represents the lithium-sulfur battery prepared in Comparative Example 1, and FAU-Bi2O3 represents the lithium-sulfur battery prepared in Example 9.

[0064] Example 10 The present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, an electrolyte, and the FAU-Bi2O3-50 catalyst-modified separator described in Example 6.

[0065] The positive electrode is composed of a composite of carbon nanotubes, acetylene black, a binder, and sublimed sulfur. Among them, by mass percentage: the carbon nanotubes are 25%, the sublimed sulfur is 60%, the acetylene black is 7%, the binder is polyvinylidene fluoride, and the binder content is 8%; The carbon nanotubes, acetylene black, and binder PVDF are mixed and ground, N-methyl-2-pyrrolidone (NMP) is added to make a slurry, and it is coated on carbon-coated aluminum foil and dried at 60 °C to obtain a lithium-sulfur positive electrode.

[0066] The negative electrode is metallic lithium.

[0067] Example 11 The present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, an electrolyte, and a modified separator loaded with the catalyst FAU-Bi2O3-50 as described in Example 6.

[0068] The positive electrode is composed of a composite of carbon nanotubes, acetylene black, a binder, and sublimed sulfur. Among them, by mass percentage: carbon nanotubes are 20%, sublimed sulfur is 60%, acetylene black is 15%, the binder is polyvinylidene fluoride, and the binder content is 15%; Mix and grind carbon nanotubes, acetylene black, and the binder PVDF, add N-methyl-2-pyrrolidone (NMP), make a slurry, and coat it on carbon-coated aluminum foil, and dry it at 60 °C to obtain a lithium-sulfur positive electrode.

[0069] The negative electrode is metallic lithium.

[0070] Example 12 The present invention provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, an electrolyte, and a modified separator loaded with the catalyst FAU-Bi2O3-50 as described in Example 6.

[0071] The positive electrode is composed of a composite of carbon nanotubes, acetylene black, a binder, and sublimed sulfur. Among them, by mass percentage: carbon nanotubes are 23%, sublimed sulfur is 55%, acetylene black is 11%, the binder is polyvinylidene fluoride, and the binder content is 11%; Mix and grind carbon nanotubes, acetylene black, and the binder PVDF, add N-methyl-2-pyrrolidone (NMP), make a slurry, and coat it on carbon-coated aluminum foil, and dry it at 60 °C to obtain a lithium-sulfur positive electrode.

[0072] In summary, the present invention provides a relay catalyst, a preparation method, and an application of a lithium-sulfur battery, aiming to improve the slow kinetics of polysulfide conversion in a lithium-sulfur battery. By reacting Bi(NO3)3 with FAU-type molecular sieve through a hydrothermal method and calcining, it is transformed into a composite structure of Bi2O3 nanosheets and FAU-type molecular sieve, so that the relay catalyst is composed of FAU molecular sieve with a rich porous structure and strong polysulfide adsorption ability and Bi2O3 that catalyzes the rapid conversion of polysulfide. The FAU molecular sieve is embedded between the Bi2O3 layer structures. In the process of polysulfide conversion, the FAU molecular sieve first captures polysulfide, and then Bi2O3 quickly catalyzes its conversion to form lithium sulfide, accelerating the kinetics and desorption process of the lithium-sulfur battery, showing good mechanical properties and effective electrolyte contact, and ensuring efficient ion transport.

[0073] The above are only the preferred embodiments of the present invention, and are not intended to limit the technical solutions of the present invention. Those skilled in the art should understand that without departing from the spirit and principle of the present invention, the technical solutions can be subject to several simple modifications and substitutions, and these modifications and substitutions also fall within the protection scope covered by the claims.

Claims

1. A method for preparing a relay catalyst for a lithium-sulfur battery, characterized in that: include: Mixing Bi(NO3)3 and FAU type molecular sieve and dispersing them in an organic mixed solvent to form a mixed liquid; hydrothermally treating the mixed solution to obtain a solid product; The solid product is calcined to obtain a lithium-sulfur battery relay catalyst.

2. The method for preparing a lithium-sulfur battery relay catalyst according to claim 1, characterized in that: The mass ratio of Bi(NO3)3 to FAU type molecular sieve is (9.7-38.8):

1.

3. The method for preparing a lithium-sulfur battery relay catalyst according to claim 1, characterized in that: The organic mixed solvent is a mixed solution of ethanol and ethylene glycol.

4. The method for preparing a lithium-sulfur battery relay catalyst according to claim 3, characterized in that: The volume ratio of the ethanol to the ethylene glycol is 2:

1.

5. The method for preparing a relay catalyst for a lithium-sulfur battery according to claim 1, characterized in that: The hydrothermal treatment is carried out at 170° C. to 190° C. for 8 to 12 hours.

6. The method for preparing a lithium-sulfur battery relay catalyst according to claim 1, characterized in that: The calcination conditions are 500° C. to 600° C. and the temperature is kept at 1 to 3 hours.

7. A lithium-sulfur battery relay catalyst, characterized in that: Prepared by the method according to any one of claims 1 to 6.

8. Use of the lithium-sulfur battery relay catalyst as claimed in claim 7 in preparing a lithium-sulfur battery separator, characterized in that: include: The lithium-sulfur battery relay catalyst, acetylene black and a binder are mixed and dispersed in an NMP solvent to form a slurry; The slurry is coated on a PP separator and dried to obtain a lithium-sulfur battery separator.

9. Use of the lithium-sulfur battery relay catalyst according to claim 8 in the preparation of a lithium-sulfur battery separator, characterized in that: The mass ratio of the lithium-sulfur battery relay catalyst, acetylene black and binder is 2:7:1; the thickness of the lithium-sulfur battery separator is 13-16 μm.

10. A lithium-sulfur battery, characterized in that: Comprising the lithium-sulfur battery separator as claimed in claim 9.

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