Preparation Method of Lithium-Sulfur Battery Based on Phosphorus-Based Anionic Framework Polymer Separator Coating

Abstract

The invention discloses a preparation method of a lithium-sulfur battery based on a phosphorous-based anion framework polymer separator coating. First, an anionic organometallic framework material is synthesized by a hydrothermal method, and it is prepared into a slurry with conductive carbon black (SuperP) and a binder (PVDF) in a certain proportion, and then coated on a commercial separator to form an anionic organometallic framework material lithium-sulfur battery separator. Finally, it is assembled with a sulfur-loaded carbon nanotube composite cathode material and a lithium metal anode to form a lithium-sulfur battery, obtaining a lithium-sulfur battery with good thermal stability, low impedance and good cycling performance. The material has a specific capacity of 1127 mAh g-1 at a rated capacitance of 0.5C and 815 mAh g-1 at a rated capacitance of 3C, and its Coulomb efficiency is close to 100%.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur battery materials, and particularly relates to a preparation method of a lithium-sulfur battery based on a phosphorous-based anion framework polymer separator coating. Background Art

[0002] The electrochemical performance of existing power batteries is to a great extent determined by the theoretical specific capacity provided by their materials. The most widely used cathode materials for existing secondary batteries include lithium manganate (LiMn2O4), lithium cobaltate (LiCoO2), ternary materials (LiNiMnCoO2), and lithium iron phosphate (LiFePO4), etc. Among them, the highest battery theoretical capacity is only 190 mAh / g, which has a relatively low battery capacity. Therefore, to a certain extent, it restricts the improvement of the energy density of lithium batteries. Therefore, for a long time, in order to improve the specific capacity of the battery, increase the energy density of the battery, reduce the manufacturing cost of the battery, improve the cycle performance of the battery, and improve the safety performance of the battery, it is necessary to find new battery materials with higher capacity. Among them, sulfur materials are generally recognized by the industry. Sulfur materials are very abundant in the earth's reserves, very easy to obtain, low in price, and basically non-toxic. The electrochemical reaction with lithium is expected to be a reversible reaction during the charge and discharge process. Therefore, lithium-sulfur batteries have become a hot topic of concern for researchers in recent years.

[0003] Lithium-sulfur batteries belong to secondary batteries and can be charged and discharged multiple times. Sulfur provides a high theoretical energy density (2600 Wh / kg) and a high theoretical specific capacity (1675 mAh / g), which is 8 to 10 times that of commercial lithium batteries. It is considered to be very promising to become one of the next-generation high-energy battery systems. Although lithium-sulfur batteries have such high energy density and theoretical capacity, it is found in the experimental process that the cycle performance of lithium-sulfur batteries is poor. Therefore, researchers have made many modification schemes on the positive and negative electrode materials, and each research material field has contributed its own strength.

[0004] In recent years, it has been gradually discovered that the separator layer is an important influencing factor in the ion conduction process between the two electrodes. Therefore, a large amount of research has been done on modifying the separator of lithium-sulfur batteries. For example, porous materials are used to add conductive agents to enhance the function of the separator in transporting ions. The composite sulfur (S) cathode in lithium-sulfur batteries serves as the cathode material of the lithium-sulfur battery, and a lithium metal sheet is used as the anode material of the lithium-sulfur battery. A separator is needed to separate the anode and cathode between the positive and negative electrodes. Currently, commonly used commercial separators are made of materials such as PP and PE. Typical PP separators include Celgard 2400, Celgard 2500, etc. They are all single-layer separators, and the porosity between them is different. The difference in porosity also affects the efficiency of lithium-ion migration. Most commercial membranes are made of polymer materials, with poor conductivity and are easily pierced by lithium dendrites, resulting in problems such as battery short circuit and poor stability. Therefore, further research is still needed in the modification of the separator. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a lithium-sulfur battery based on a phosphorous-based anion framework polymer separator, which solves the problems of poor conductivity and poor thermal stability of the existing lithium-sulfur battery separator.

[0006] The technical solution adopted by the present invention is a method for preparing a lithium-sulfur battery based on a phosphorous-based anion framework polymer separator. The specific operation steps are as follows:

[0007] Step 1: Weigh zinc nitrate hexahydrate solid and pentamethyltetrazole powder in sequence. Add the two into a polytetrafluoroethylene reaction kettle containing N,N-dimethylformamide solution, and then add phosphorous acid solution. Stir at room temperature until the solution is uniformly transparent. Place it in the reaction kettle and react at 85 °C for 3 days. Then wash it with methanol, wash at least three times, and centrifuge and dry to obtain a phosphorous-based anion framework metal tetrazole crystalline material A;

[0008] Step 2: Mix the phosphorous-based anion framework metal tetrazole crystalline material A, conductive carbon black, and binder obtained in Step 1 in an agate mortar and grind them forcefully. Then continue to add N-methylpyrrolidone to the mortar until a uniform and slightly viscous black slurry B is formed;

[0009] Step 3: After cutting the separator, fix it on a clean and flat glass plate disinfected with alcohol. Use a film scraper to scrape the black slurry B obtained in Step 2 on the surface of the separator. Transfer the obtained modified separator together with the glass plate to a vacuum drying oven for drying to obtain a uniform modified separator C;

[0010] Step 4: Take out the modified separator C obtained in Step 3 and cut the separator C into circular pieces with a tablet press to obtain a modified battery separator D;

[0011] Step 5: The modified battery separator D obtained in Step 4 is separately packed into a plastic-sealed bag and placed in a vacuum drying oven to obtain a lithium-sulfur battery separator E made of a phosphorous-based anionic metal-organic framework material;

[0012] Step 6: The battery separator E obtained in Step 5 is assembled with a sulfur-loaded carbon nanotube composite cathode material and a lithium metal anode to form a lithium-sulfur battery, and the rate performance, impedance, and cyclic voltammetry (CV) are tested at different currents.

[0013] The features of the present invention also lie in that,

[0014] In Step 1, the mass ratio of zinc nitrate hexahydrate solid to pentamethyltetrazole powder is 12:5, and the volume ratio of phosphorous acid solution to solvent N,N-dimethylformamide solution is 100:3.

[0015] The zinc nitrate hexahydrate solid described in Step 1 can be replaced by any one of zinc chloride and zinc acetate.

[0016] In Step 2, the mass ratio of the anionic framework metal tetrazole crystalline material A, conductive carbon black, and binder is 8:1:1, and the grinding time is at least 30 min.

[0017] The vacuum drying temperature in Step 3 is 60°C to 70°C, and the drying time is not less than 12 h.

[0018] The diameter of the cut piece in Step 4 is 16 mm.

[0019] The vacuum drying temperature in Step 5 is 60 - 70°C, and the drying time is 8 - 12 h.

[0020] In Step 6, when assembling the lithium-sulfur battery to test the electrochemical performance: the rate performance is tested at different currents, and the currents are set to 0.5C, 1C, 2C, 3C, 5C. When testing the electrochemical impedance (EIS), the test parameter frequency is 0.01 - 1000000 Hz, and when testing by cyclic voltammetry, the test voltage is 1.7V - 2.7V, and the scanning rate is 0.001V / s.

[0021] The separator model described in Step 3 is the Celgard 2400 separator.

[0022] The synthesis principle of the key steps in the present invention:

[0023] (I) Synthesis of the phosphorous-based anionic framework metal tetrazole crystalline material: The anionic framework metal tetrazole crystalline material powder A is characterized in that negative charges are introduced by phosphorous acid during the synthesis process, so that the prepared metal tetrazole crystalline material is negatively charged. Using the negatively charged material for the lithium-sulfur battery separator layer is beneficial to adsorb Li + , improving the transference number of Li + between the positive and negative electrodes, and thus improving the electrochemical performance of the lithium-sulfur battery.

[0024] (2) Preparation of the lithium-sulfur diaphragm coating of the pre-treated phosphorous-based anion framework polymer battery: Select the Celgard 2400 diaphragm as the substrate of the lithium-sulfur battery diaphragm. On the one hand, due to its porosity, the diaphragm modification material can be evenly attached to the surface. On the other hand, compared with other PP-type diaphragms, the Celgard 2400 diaphragm is conducive to processing and has a high cost performance.

[0025] Preparation method of the lithium-sulfur battery diaphragm based on the phosphorous-based anion framework material: The anion framework metal tetrazole crystalline material A synthesized from zinc nitrate hexahydrate [Zn(NO3)2·6(H2O)] solid and pentamethyltetrazole (5-MTZ) powder has good thermal stability, and there are a large number of mesopores and micropores, with a super-high specific surface area, which is conducive to the rapid transmission of lithium ions and improves the cycling characteristics of the lithium-sulfur battery. It is prepared into a slurry and scrape-coated on the surface of the Celgard 2400 diaphragm, and such a modified diaphragm has better properties.

[0026] The preparation method of the lithium-sulfur battery based on the phosphorous-based anion framework polymer diaphragm of the present invention uses the scraping method to scrape the anion framework diaphragm coating on the Celgard 2400 diaphragm. At a current density of 0.5C, there is an initial capacity of 1127 mAh·g -1 and has a rate performance of up to 5C.

[0027] The beneficial effects of the present invention are:

[0028] (1) Four nitrogen atoms in the ligand pentamethyltetrazole in the phosphorous-based anion framework metal tetrazole crystalline material A prepared by the hydrothermal method can have a strong coordination effect with metal zinc, obtaining a crystalline material with good thermal stability. Such a highly crystalline negative charge framework is conducive to the conduction of lithium ions.

[0029] (2) The slurry prepared from the phosphorous-based anion framework metal tetrazole crystalline material is scrape-coated on the surface of the Celgard 2400 diaphragm by the scraping method to construct an anion-type organic metal framework material lithium-sulfur battery diaphragm. The composite diaphragm prepared by a simple method combines the advantages of the properties of the two materials. This method is simple and easy to implement, and is not only applicable to the general Celgard 2400 diaphragm, but can also be used for the modification of other battery diaphragms. The composite diaphragm material can not only be used for the modification of lithium-sulfur batteries, but also for the modification of diaphragms of other solid-state batteries, with a wide range of applications. Description of the Drawings

[0030] Figure 1 is the flow chart of the preparation method of the lithium-sulfur battery based on the phosphorous-based anion framework polymer diaphragm of the present invention;

[0031] Figure 2It is the X-ray diffraction pattern of the phosphorus-based anionic framework crystal material of the present invention;

[0032] Figure 3 It is the relationship diagram (CV) of current density and potential of the lithium-sulfur battery (PO3-LSBs) of the present invention;

[0033] Figure 4 It is the electrochemical impedance (EIS) of the lithium-sulfur battery of the present invention.

[0034] Figure 5 It is the rate performance diagram of the lithium-sulfur battery of the present invention at different currents.

[0035] Figure 6 It is the relationship diagram of efficiency and specific capacity of the lithium-sulfur battery of the present invention after 300 cycles at a rated capacitance of 3C. Detailed implementation manners

[0036] The preparation method of the lithium-sulfur battery based on the phosphorus-based anionic framework polymer separator provided by the present invention includes the synthesis of the phosphorus-based anionic framework material. By blending it with conductive carbon black (SuperP) and binder PVDF, a slurry is prepared and scraped on a celgard2400 separator to obtain a modified separator, and it is assembled with a sulfur positive electrode and a lithium negative electrode to form a lithium-sulfur battery.

[0037] The present invention will be further described below in conjunction with specific embodiments.

[0038] Example 1:

[0039] The preparation method of the lithium-sulfur battery based on the phosphorus-based anionic framework polymer separator of the present invention has a process as Figure 1 shown, and the specific operation steps are as follows:

[0040] Step 1: Weigh solid zinc nitrate hexahydrate [Zn(NO3)2·6(H2O)] and 5-methyltetrazole (5-MTZ) powder (mass ratio 12:5) in sequence. Add the two into a polytetrafluoroethylene reaction kettle containing 5 mL of N,N-dimethylformamide (DMF) solution, and then add 3 drops of phosphorous acid (H3PO3) solution. Stir at room temperature until the solution is uniformly transparent, place it in the reaction kettle at 85 °C for 3 days, then wash with methanol, wash at least three times, and centrifuge and dry to obtain white anionic framework-type metal tetrazole crystalline material A;

[0041] Step 2: Mix the anionic framework-type metal tetrazole crystalline material A, conductive carbon black (SuperP), and binder (PVDF) obtained in Step 1 (mass ratio 8:1:1), and grind them forcefully in an agate mortar for 30 min. Continue to add N-methylpyrrolidone (NMP) to the mortar until a uniform and slightly viscous black slurry B is formed;

[0042] Step 3: After cutting the commercial separator Celgard 2400, fix it on a clean and flat glass plate disinfected with alcohol. Use a film scraper to scrape the black slurry B obtained in Step 2 on the surface of the Celgard 2004 separator. Transfer the obtained modified separator together with the glass plate to a vacuum drying oven at 60°C and dry for 12 h to obtain a uniform modified separator C;

[0043] Step 4: Take out the modified separator C obtained in Step 4, and use a tablet press to cut the separator C into circular pieces with a diameter of 16 mm to obtain a modified battery separator D;

[0044] Step 5: Separate and pack the modified battery separator D obtained in Step 4 into plastic-sealed bags, and place them in a vacuum drying oven at 60°C and dry for 12 h to obtain an anion-type metal-organic framework material lithium-sulfur battery separator E.

[0045] Step 6: Assemble the battery separator E obtained in Step 5 with the S@CNT composite positive electrode material and the negative electrode material lithium sheet into a lithium-sulfur battery, and test the rate performance (at currents of 0.5C, 1C, 2C, 3C, 5C), impedance (frequency of 0.01 - 1000000 Hz), and CV (1.7V - 2.7V, scanning rate of 0.001V / s) at different currents.

[0046] Example 2:

[0047] Step 1: Weigh solid zinc chloride (ZnCl2) and 5-methyltetrazole (5-MTZ) powder (mass ratio 12:5) in sequence, add the two to a polytetrafluoroethylene reaction kettle containing 5 mL of N,N-dimethylformamide (DMF) solution, continue to add 3 drops of phosphorous acid (H3PO3) solution, stir at room temperature until the solution is uniformly transparent, place it in the reaction kettle and react at 85°C for 3 days, then wash with methanol, wash at least three times, and centrifuge and dry to obtain a white phosphorous-based anion framework-type metal tetrazole crystalline material A;

[0048] Step 2: Mix the phosphorous-based anion framework-type metal tetrazole crystalline material A, conductive carbon black (SuperP), and binder (PVDF) obtained in Step 1 (mass ratio 8:1:1) and grind them forcefully in an agate mortar for 30 min. Continue to add N-methylpyrrolidone (NMP) to the mortar until a uniform and slightly viscous black slurry B is formed;

[0049] Step 3: After cutting the commercial separator Celgard 2400, fix it on a clean and flat glass plate disinfected with alcohol. Use a film scraper to scrape the black slurry B obtained in Step 2 on the surface of the Celgard 2004 separator. Transfer the obtained modified separator together with the glass plate to a vacuum drying oven at 60°C and dry for 12 h to obtain a uniform modified separator C;

[0050] Step 4: Take out the modified separator C obtained in Step 4, and use a tablet press to cut the separator C into circular pieces with a diameter of 16 mm to obtain a modified battery separator D;

[0051] Step 5: Separate and load the modified battery separator D obtained in Step 4 into plastic-sealed bags, and place them in a vacuum drying oven at 60 °C for 12 h to obtain a phosphorous-based anionic metal-organic framework material lithium-sulfur battery separator E.

[0052] Step 6: Assemble the battery separator E obtained in Step 5 with the S@CNT composite positive electrode material and the negative electrode material lithium sheet into a lithium-sulfur battery, and test the rate performance (at currents of 0.5C, 1C, 2C, 3C, 5C), impedance (frequency of 0.01 - 1000000 Hz), and CV (1.7V - 2.7V, scan rate of 0.001V / s) at different currents.

[0053] Example 3:

[0054] Step 1: Weigh solid zinc nitrate hexahydrate [Zn(NO3)2·6(H2O)] and 5-methyltetrazole (5-MTZ) powder (mass ratio 2:1) in sequence, add the two into a polytetrafluoroethylene reaction kettle containing 5 mL of N,N-dimethylformamide (DMF) solution, continue to add 3 drops of phosphorous acid (H3PO3) solution, stir at room temperature until the solution is uniformly transparent, place it in the reaction kettle and react at 85 °C for 3 days, then wash with methanol, wash at least three times, and centrifuge and dry to obtain a phosphorous-based white anionic framework metal tetrazole crystalline material A;

[0055] Step 2: Mix the phosphorous-based anionic framework metal tetrazole crystalline material A, conductive carbon black (SuperP), and binder (PVDF) obtained in Step 1 (mass ratio 8:1:1) and grind them forcefully in an agate mortar for no less than 30 min. Continue to add N-methylpyrrolidone (NMP) to the mortar until a uniform and slightly viscous black slurry B is formed;

[0056] Step 3: After cutting the commercial separator celgard2400, fix it on a clean and flat glass plate disinfected with alcohol. Use a film scraper to scrape the black slurry B obtained in Step 2 on the surface of the celgard2004 separator. Transfer the obtained modified separator together with the glass plate to a vacuum drying oven at 60 °C and dry for 12 h to obtain a uniform modified separator C;

[0057] Step 4: Take out the modified separator C obtained in Step 4, and use a tablet press to cut the separator C into circular pieces with a diameter of 16 mm to obtain a modified battery separator D;

[0058] Step 5: Separate the modified battery separator D obtained in Step 4 and pack it into plastic-sealed bags. Then place it in a vacuum drying oven at 60 °C for 12 h to obtain a lithium-sulfur battery separator E made of a phosphorous-based anionic organic metal framework material.

[0059] Step 6: Assemble the battery separator E obtained in Step 5, the S@CNT composite cathode material, and the lithium metal anode into a lithium-sulfur battery, and test its rate performance (at currents of 0.5C, 1C, 2C, 3C, and 5C), impedance (at a frequency of 0.01 - 1000000 Hz), and CV (from 1.7 V to 2.7 V with a scan rate of 0.001 V / s).

[0060] Example 4:

[0061] Step 1: Weigh solid zinc nitrate hexahydrate [Zn(NO3)2·6(H2O)] and 5-methyltetrazole (5-MTZ) powder in a mass ratio of 12:5 in sequence. Add the two to a polytetrafluoroethylene reaction kettle containing 5 mL of N,N-dimethylformamide (DMF) solution, and then add 3 drops of phosphorous acid (H3PO3) solution. Stir at room temperature until the solution is uniformly transparent, place the reaction kettle in an oven at 100 °C for 2 days, then wash with methanol at least three times, and centrifuge and dry to obtain a white crystalline material A of a phosphorous-based anionic framework metal tetrazole.

[0062] Step 2: Mix the crystalline material A of the phosphorous-based anionic framework metal tetrazole obtained in Step 1, conductive carbon black (SuperP), and binder (PVDF) in a mass ratio of 7:2:1 and grind them forcefully in an agate mortar for no less than 30 min. Then continue to add N-methylpyrrolidone (NMP) to the mortar until a uniform and slightly viscous black slurry B is formed.

[0063] Step 3: After cutting the commercial separator celgard2400, fix it on a clean and flat glass plate disinfected with alcohol. Use a film scraper to scrape the black slurry B obtained in Step 2 onto the surface of the celgard2004 separator. Transfer the obtained modified separator together with the glass plate to a vacuum drying oven at 60 °C for 12 h to obtain a uniform modified separator C.

[0064] Step 4: Take out the modified separator C obtained in Step 4, and use a tablet press to cut the separator C into circular pieces with a diameter of 16 mm to obtain a modified battery separator D.

[0065] Step 5: Separate the modified battery separator D obtained in Step 4 and pack it into plastic-sealed bags. Then place it in a vacuum drying oven at 60 °C for 12 h to obtain a lithium-sulfur battery separator E made of a phosphorous-based anionic organic metal framework material.

[0066] Step 6: Assemble the battery separator E obtained in Step 5, the S@CNT composite cathode material, and the anode material lithium sheet into a lithium-sulfur battery, and test the rate performance (currents of 0.5C, 1C, 2C, 3C, 5C), impedance (frequency of 0.01 - 1000000 Hz), and CV (1.7V - 2.7V, scan rate of 0.001V / s) at different currents.

[0067] Example 5:

[0068] Step 1: Weigh solid zinc nitrate hexahydrate [Zn(NO3)2·6(H2O)] and 5-methyltetrazole (5-MTZ) powder in sequence (mass ratio 12:5). Add the two into a polytetrafluoroethylene reaction kettle containing 5 mL of N,N-dimethylformamide (DMF) solution, then add 3 drops of phosphorous acid (H3PO3) solution. Stir at room temperature until the solution is uniformly transparent, place it in the reaction kettle and react at 85°C for 3 days, then wash with methanol, wash at least three times, and centrifuge and dry to obtain the phosphorus-based white anion framework type metal tetrazole crystalline material A.

[0069] Step 2: Mix the phosphorus-based anion framework type metal tetrazole crystalline material A, conductive carbon black (SuperP), and binder (PVDF) obtained in Step 1 (mass ratio 8:1:1), and grind them forcefully in an agate mortar for 40 min. Then continue to add N-methylpyrrolidone (NMP) to the mortar until a uniform and slightly viscous black slurry B is formed.

[0070] Step 3: After cutting the commercial separator celgard2400, fix it on a clean and flat glass plate disinfected with alcohol. Use a film scraper to scrape the black slurry B obtained in Step 2 on the surface of the celgard2004 separator. Transfer the obtained modified separator together with the glass plate to a vacuum drying oven at 70°C and dry for 8 h to obtain a uniform modified separator C.

[0071] Step 4: Take out the modified separator C obtained in Step 4, and use a tablet press to cut the separator C into circular pieces with a diameter of 16 mm to obtain a modified battery separator D.

[0072] Step 5: Separate the modified battery separator D obtained in Step 4 and put it into a plastic-sealed bag, then place it in a vacuum drying oven at 70°C and dry for 8 h to obtain the phosphorus-based anion type organometallic framework material lithium-sulfur battery separator E.

[0073] Step 6: Assemble the battery separator E obtained in Step 5, the S@CNT composite cathode material, and the anode material lithium sheet into a lithium-sulfur battery, and test the rate performance (currents of 0.5C, 1C, 2C, 3C, 5C), impedance (frequency of 0.01 - 1000000 Hz), and CV (1.7V - 2.7V, scan rate of 0.001V / s) at different currents.

[0074] like Figure 2 The figure shows the X-ray diffraction pattern of the phosphorus-based anionic organic metal framework material (PO3). According to the XRD pattern, it can be clearly seen that the crystal peaks of the crystalline material are basically consistent with the standard curve. This also proves that the phosphorus-based anionic organic metal framework material (PO3) has been successfully prepared.

[0075] like Figure 3 As shown, the lithium-sulfur battery (PO3-LSB) assembled with a phosphorus-based anion organic metal framework lithium-sulfur battery separator at a scan rate of 0.001 V / s S The relationship between current density and potential (CV curve) of the material has a pair of redox peaks. It reveals the redox reaction of S during the charge and discharge process of the material and has good electrochemical activity.

[0076] like Figure 4 As shown, the lithium-sulfur battery (PO3-LSB) assembled with the phosphorus-based anion organic metal framework material lithium-sulfur battery separator of the present invention S ) electrochemical impedance spectroscopy (EIS). The charge transfer resistance and Warburg impedance of the material can be determined by the semicircle of the EIS curve in the high-frequency region and the oblique line in the low-frequency region. EIS curves are usually used to evaluate the performance of electrochemical resistance and capacitance. The radius of the semicircle of the impedance spectrum represents the interface resistance of the electrolyte and the electrode. Intuitively, the larger the semicircle in the impedance graph, the greater the impedance, and the worse the electrochemical performance of the battery. Figure 4 It can be seen intuitively that the battery has a smaller electrochemical impedance.

[0077] like Figure 5 As shown, the lithium-sulfur battery (PO3-LSB) assembled with the phosphorus-based anion organic metal framework material lithium-sulfur battery separator of the present invention S ) rate. The rate diagram can be used to obtain the battery specific capacity of lithium-sulfur batteries at different currents. Compared with lithium-sulfur batteries prepared by traditional methods, lithium-sulfur batteries (PO3-LSB S ) has a higher specific capacity at a large rated capacity of 1C, 2C, 3C or even 5C.

[0078] like Figure 6 As shown, the lithium-sulfur battery (PO3-LSB) assembled with the phosphorus-based anion organic metal framework material lithium-sulfur battery separator of the present invention SThe long-cycle graph of specific capacity. The long-cycle graph of specific capacity is used to evaluate the change in the specific capacity of the battery and the retention of Coulombic efficiency after several charge-discharge cycles. Coulombic efficiency is the ratio of the discharge capacity of the battery to the charge capacity during the same cycle. Theoretically, the closer the charge and discharge capacities are, the better the electrochemical performance of the battery. In the graph, the battery still maintains a specific capacity of 580 mAh / g after 300 cycles at 3C capacitance, and the Coulombic efficiency is close to 100% during the cycle.

Claims

1. Preparation method of lithium-sulfur battery based on phosphorous-based anion framework polymer separator coating, characterized in that, The specific operation steps are as follows: Step 1: Weigh zinc nitrate hexahydrate solid and pentamethyltetrazole powder in sequence, add the two into a polytetrafluoroethylene reaction kettle containing N,N-dimethylformamide solution, continue to add phosphorous acid solution, stir at room temperature until the solution is uniformly transparent, place it in the reaction kettle and react at 85 °C for 3 days, then wash with methanol, wash at least three times, centrifuge and dry to obtain a phosphorous-based anion framework type metal tetrazole crystalline material A; In Step 1, the mass ratio of zinc nitrate hexahydrate solid to pentamethyltetrazole powder is 12:5, and the volume ratio of phosphorous acid solution to the solvent N,N-dimethylformamide solution is 100:3; In Step 1, the zinc nitrate hexahydrate described can be replaced by any one of zinc chloride and zinc acetate; Step 2: Mix the phosphorous-based anion framework type metal tetrazole crystalline material A, conductive carbon black and binder obtained in Step 1 and grind them in an agate mortar, continue to add N-methylpyrrolidone to the mortar until a uniform and slightly viscous black slurry B is formed; In Step 2, the mass ratio of the anion framework type metal tetrazole crystalline material A, conductive carbon black and binder is 8:1:1, and the grinding time is at least 30 min; Step 3: After cutting the celgard2400 separator, fix it on a clean and flat glass plate disinfected with alcohol, use a film scraper to scrape the black slurry B obtained in Step 2 on the surface of the separator, transfer the obtained modified separator together with the glass plate to a vacuum drying oven for drying to obtain a uniform modified separator C; The vacuum drying temperature in Step 3 is 60 °C - 70 °C, and the drying time is not less than 12 h; Step 4: Take out the modified separator C obtained in Step 3, use a tablet press to cut the separator C into round pieces to obtain a modified battery separator D; Step 5: Separate the modified battery separator D obtained in Step 4 and put it into a plastic-sealed bag, and put it into a vacuum drying oven to obtain a phosphorous-based anion type organometallic framework material lithium-sulfur battery separator E; Step 6: Assemble the battery separator E obtained in Step 5 with a sulfur-loaded carbon nanotube composite positive electrode material and a negative electrode material lithium sheet into a lithium-sulfur battery, and test the rate performance, impedance, and CV at different currents.

2. The preparation method of the lithium-sulfur battery based on the phosphorous-based anion framework polymer separator coating according to claim 1, characterized in that The diameter of the cut piece in Step 4 is 16 mm.

3. The method for preparing a lithium-sulfur battery based on a phosphorous-based anion framework polymer separator coating according to claim 1, wherein The vacuum drying temperature in Step 5 is 60 - 70 °C, and the drying time is 8 - 12 h.

4. The preparation method of the lithium-sulfur battery based on the phosphorous-based anion framework polymer separator coating according to claim 1, wherein In Step 6, when assembling the lithium-sulfur battery to test the electrochemical performance: test the rate performance at different currents, the currents are set to 0.5C, 1C, 2C, 3C, 5C, the parameter frequency tested when testing the electrochemical impedance is 0.01 - 1000000 Hz, and the voltage for cyclic voltammetry testing is 1.7V - 2.7V, and the scanning rate is 0.001V / s.

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