Method for covalently binding double-bond-containing metal coordination polymer with sulfur molecules and application of double-bond-containing metal coordination polymer in positive electrode of lithium-sulfur battery

Abstract

The invention discloses a method for covalently binding a double-bond-containing metal coordination polymer with sulfur molecules and application of the double-bond-containing metal coordination polymer in a positive electrode of a lithium-sulfur battery, and belongs to the technical field of lithium-sulfur batteries. The preparation method comprises the following steps: reacting acryloyl chloride with amino groups on tetraaminobenzene to obtain double-bond modified BTA molecules, adding bacterial cellulose turbid liquid, then adding a nickel chloride hexahydrate aqueous solution, stirring, dropwise adding stronger ammonia water to initiate coordination polymerization, washing and freeze-drying to obtain BTA-ACry-Ni-coated BC aerogel; and enabling elemental sulfur and the BTA-ACry-Ni-BC aerogel to trigger sulfur vapor molecule ring opening at a high temperature under the condition that the elemental sulfur and the BTA-ACry-Ni-BC aerogel are not in contact with each other, and then reacting with double bonds to obtain the BTA-ACry-Ni-BC-S composite material covalently bound with sulfur molecules. The prepared sulfur covalent binding metal coordination polymer plays an important role in inhibiting dissolution of polysulfide and accelerating conversion of active substances, and is beneficial to preparation of advanced energy storage devices with large energy storage capacity, high coulombic efficiency and long cycle life.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, specifically relating to a method for covalently binding sulfur molecules with a double-bonded metal coordination polymer and its application in the positive electrode of a lithium-sulfur battery. Background Technology

[0002] Natural energy sources, such as wind and solar power, are characterized by significant spatiotemporal discontinuity, posing high demands on large-capacity, high-efficiency, and long-life energy storage technologies. Currently, lithium-ion battery electrochemical energy storage technology has been successfully commercialized in portable electronic products and some electric transportation applications. However, lithium-ion batteries, based on the fundamental chemical principle of ion intercalation, have reached their theoretical limits in terms of energy density and specific capacity, making it difficult to meet the energy storage requirements for large-scale natural energy sources. Lithium-sulfur batteries have a theoretical energy density more than six times that of ordinary lithium-ion batteries. Furthermore, elemental sulfur, the main active material in lithium-sulfur batteries, is abundant, inexpensive, and non-toxic in the Earth's crust, and lithium-sulfur batteries also exhibit stable discharge voltages. Therefore, lithium-sulfur batteries have become one of the important candidate systems for large-capacity, large-scale energy storage. However, lithium-sulfur batteries still face many challenges in commercial development. Among them, the dissolution and diffusion of polysulfides in the electrolyte (shuttle effect) leads to rapid capacity decay and low coulombic efficiency, thus becoming a key problem that urgently needs to be solved.

[0003] Sulfur molecules covalently bonded to the substrate are considered to effectively suppress the dissolution and shuttle of sulfur during charge / discharge. Xun et al. covalently polymerized resveratrol allyl ether with elemental sulfur, and the resulting sulfur-rich polymer was successfully used in the cathode of a high-performance lithium-sulfur battery (Data source: Xingwei Xun, Dongping Chen, Xi-Cun Wang, Xiaofeng Wu, Zheng-Jun Quan, Novel Resveratrol-Derived Sulfur-Rich Polymers: Advanced Materials for Silver Capture and High-Performance Lithium-SulfurBattery Cathodes, ACS Sustainable Chemistry & Engineering, November 7, 2024.DOI: 10.1021 / acssuschemeng.4c06786). Chang et al. synthesized a novel mesoporous hollow sulfurized aminophenol-formaldehyde resin active composite material in which sulfur molecules are covalently linked in the form of short chains, thereby effectively suppressing the shuttle effect of polysulfides (Data source: Wei Chang, Jin Qu, Yanqiu Sui, Qiu-Yu Ji, Ting-TingZhang, Xian-Zhi Zhai, Ya-Qiong Jing, Zhong-Zhen Yu, Constructing mesoporoushollow polysulfane spheres bonded with short-chain sulfurs (Sx, x≤3) as high-performance sulfur cathodes in both ether and ester electrolytes, EnergyStorage Materials, 27 (2020) 426-434). Furthermore, certain metallic substances can achieve highly efficient catalytic conversion of sulfur-containing active materials, thereby shortening the residence time of soluble polysulfides in the electrolyte, which can also suppress the shuttle effect to some extent.

[0004] Tetraaminobenzene-nickel (BTA-Ni) metal coordination polymers, due to the abundance of amino groups on their molecular chains, exhibit strong polar interactions with soluble polysulfides and contribute to the stable and rapid conduction of lithium ions. In addition to controlling polysulfides, the coordinating metal Ni in BTA-Ni can accelerate the redox conversion of polysulfides through electrocatalysis, improving the reaction kinetics of lithium-sulfur batteries. Furthermore, BTA-Ni, with its π-d conjugated electronic structure, also exhibits electronic conductivity. However, while the physical combination of BTA-Ni and elemental sulfur to prepare lithium-sulfur battery cathodes can improve battery performance to some extent, the control and catalytic effect on polysulfides still depend on the random collisional contact between soluble polysulfides and the Ni metal junction. Furthermore, non-covalently bonded sulfur molecules cannot inhibit the dissolution behavior of polysulfides at the source (data from: Jing Chen, Peng Xue, Jiaqi Xu, WeiyaWang, Zixia Lin, Cheng Chu and Yang Huang, Lithium-sulfur battery cathode with sulfurized bacterial cellulose and metal-coordinated polymers to strengthen stress and promote sulfur utilization, J. Mater. Chem. A, 2026, 14, 4595). Therefore, there is an urgent need to develop a lithium-sulfur battery cathode material with high energy density and long cycle life for electrochemical energy storage devices. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for covalently binding sulfur molecules with a metal coordination polymer containing double bonds. This method can effectively inhibit the dissolution and diffusion of sulfur-containing active substances through covalent bonding and metal catalysis, and can better suppress the shuttle effect of polysulfides. Another technical problem to be solved by the present invention is to provide the application of the metal coordination polymer covalently bound sulfur molecule material in the positive electrode of lithium-sulfur batteries.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for covalently binding sulfur molecules to a double-bonded metal coordination polymer includes the following steps:

[0008] 1) Dissolve tetraaminobenzene in an aqueous solution containing potassium carbonate and sodium nitrite, add acryloyl chloride under low temperature conditions, filter, and obtain BTA-ACry;

[0009] 2) Dissolve the BTA-ACry obtained in step 1) in water, add bacterial cellulose suspension dropwise and stir to mix, then add nickel chloride hexahydrate aqueous solution, stir and add concentrated ammonia water dropwise to initiate coordination polymerization, wash and freeze dry to obtain BTA-ACry-Ni@BC aerogel.

[0010] 3) Elemental sulfur and the BTA-ACry-Ni@BC aerogel obtained in step 2) are placed in a reaction vessel without contact between them and reacted at high temperature to obtain the BTA-ACry-Ni@BC-S composite material.

[0011] Furthermore, in step 1), the low temperature condition is -5℃.

[0012] Furthermore, in step 2), the solid content of the bacterial cellulose suspension is 5-10 mg / mL.

[0013] Furthermore, in step 2), the concentration of the nickel chloride hexahydrate aqueous solution is 2-8 mg / mL.

[0014] Furthermore, in step 3), the high-temperature reaction temperature is 150-250℃.

[0015] Furthermore, the composite material of metal coordination polymer covalently bonded to sulfur molecules prepared by the method of covalently bonding sulfur molecules to double-bonded metal coordination polymers is obtained.

[0016] Furthermore, the application of the metal-coordinated polymer covalently bonded sulfur molecules composite material in the positive electrode of lithium-sulfur batteries.

[0017] Further, the process includes the following steps: mixing a composite material of metal coordination polymer covalently bonded to sulfur molecules, Super P, and PVDF, then adding NMP solvent and stirring; coating the prepared electrode slurry onto conductive carbon cloth, drying it under vacuum, and then cutting the carbon cloth electrode sheet into a circular piece; finally, using lithium metal as the negative electrode and Celgard 2250 as the separator, assembling it together with the prepared carbon cloth positive electrode into a CR2032 coin cell.

[0018] Furthermore, the mass ratio of the composite material of metal coordination polymer covalently bonded to sulfur molecules, Super P, and PVDF is 6:3:1.

[0019] Furthermore, the initial discharge specific capacity is 1208~1325 mAh / g; the discharge specific capacity after 100 cycles is 821~969 mAh / g; the discharge specific capacity after 500 cycles is 589~796 ​​mAh / g; and the average coulombic efficiency is 95.8~99.2%; Li + The diffusion coefficient is 6.36 × 10⁻⁶. -5 ~1.22×10 -4 cm2 / s.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) This invention utilizes high-temperature heating to generate sulfur vapor, which simultaneously causes the S8 molecule to open its ring and react with the double bonds on the surface of BTA-ACry-Ni@BC to form a covalent bond. Since the sulfur vapor can fully and uniformly combine with the BTA-ACry-Ni@BC aerogel, the sulfur in the reaction product BTA-ACry-Ni@BC-S is relatively uniformly distributed.

[0022] (2) This invention designs a lithium-sulfur battery cathode composite material based on metal coordination polymer (BTA-Ni). The amino groups on the BTA-Ni molecule not only provide reaction sites for modifying double bonds, but also promote the rapid and stable conduction of lithium ions. This has a beneficial effect on improving battery reaction kinetics and inhibiting dendrite growth.

[0023] (3) The present invention designs a lithium-sulfur battery cathode composite material based on metal coordination polymer (BTA-Ni). The metal nodes Ni on the BTA-Ni molecule can not only control the diffusion of polysulfides through polar interactions, but also accelerate the oxidation / reduction conversion of polysulfides through electrocatalysis initiated by metal Ni.

[0024] (4) The sulfur-containing active material prepared in the present invention in a covalently bonded form plays an important role in inhibiting the dissolution of polysulfides and accelerating the conversion of active materials, which is conducive to the preparation of advanced energy storage devices with large energy storage capacity, high coulombic efficiency and long cycle life. Attached Figure Description

[0025] Figure 1 The reaction equation for the reaction between ACry and the amino groups in the BTA molecule to obtain the double-bond modified product BTA-ACry is as follows:

[0026] Figure 2 For Ni in the aqueous solution of this application 2+ The reaction equation that initiates the coordination polymerization of BTA-ACry molecules;

[0027] Figure 3 This is the reaction equation for the reaction between the S8 molecule and the double bond in BTA-ACry-Ni after ring opening at high temperature in this application. Detailed Implementation

[0028] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0029] The elemental sulfur used in the following examples and comparative examples is sublimed sulfur; the electrolyte solvent used in the battery is a mixture of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1; the electrolyte is 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); 1 wt% lithium nitrate (LiNO3) is used as an additive in the electrolyte; the lithium-sulfur battery separator is a Celgard 2250 separator; and lithium metal sheets are used as the negative electrode of the lithium-sulfur battery.

[0030] The tetraaminobenzene (BTA) and acryloyl chloride (ACry) used in the following examples were purchased from Tianjin Xiens Biochemical Technology Co., Ltd.; bacterial cellulose (BC) was purchased from Yichang Nanomaterials Technology (Guangdong) Co., Ltd.

[0031] This application provides a method for covalently binding sulfur molecules to a metal coordination polymer, comprising the following steps:

[0032] 1) Tetraaminobenzene was dissolved in an aqueous solution containing potassium carbonate and sodium nitrite. Acryloyl chloride was added at -5°C to react with the solution. After filtration, BTA-ACry was obtained. Figure 1 );

[0033] 2) Dissolve the BTA-ACry obtained in step 1) in water, add bacterial cellulose suspension with a solid content of 5-10 mg / mL dropwise while stirring and mixing, then add nickel chloride hexahydrate aqueous solution with a concentration of 2-8 mg / mL, stir, and then add concentrated ammonia water dropwise to initiate coordination polymerization. After washing and freeze-drying, BTA-ACry-Ni@BC aerogel is obtained. Figure 2 );

[0034] 3) Elemental sulfur and the BTA-ACry-Ni@BC aerogel obtained in step 2) are placed in a reaction vessel without contact and reacted at 150-250℃ to obtain the BTA-ACry-Ni@BC-S composite material. Figure 3 ).

[0035] Example 1

[0036] A method for covalently binding sulfur molecules to a double-bonded metal coordination polymer includes the following steps:

[0037] (1) Dissolve 0.79 g K2CO3 in 10 mL deionized water, add 100 mg BTA to the solution and stir continuously for 10 min, then add 0.02 g NaNO2 and stir continuously for 5 min. Continue stirring the mixture in a low-temperature (-5℃) reaction bath, while adding excess ACry (1 mL), and continue stirring at -5℃ for 3 h. Then transfer the reaction solution to room temperature and continue stirring for 24 h. Add the reaction mixture to 50 mL ethanol and filter out the precipitate. Slowly add the obtained clear filtrate to 100 mL diethyl ether solvent, seal and maintain at 4℃ for 48 h. Filter out the solid product precipitated in the diethyl ether solvent to obtain BTA-ACry.

[0038] (2) Dissolve 40 mg of the solid product (BTA-ACry) obtained in step (1) in 10 mL of deionized water. Add the solution dropwise to 10 mL of BC suspension with a solid content of 10 mg / mL and stir vigorously for 2 h. Add 10 mL of NiCl2·6H2O aqueous solution with a concentration of 2 mg / mL to the mixture and stir continuously for 2 h. Then slowly add 2 mL of concentrated ammonia (13.38 mol / L) to initiate the metal coordination polymerization reaction. After reacting overnight, wash the precipitate thoroughly and freeze-dry it to obtain BTA-ACry-Ni@BC aerogel.

[0039] (3) Add 2.5g of elemental sulfur and 50mg of BTA-ACry-Ni@BC aerogel to a 50mL reactor, ensuring that they do not come into contact with each other. After sealing the reactor, maintain the temperature at 190℃ for 12h. After cooling, the BTA-ACry-Ni@BC-S composite material covalently bonded to sulfur molecules is obtained.

[0040] Example 2

[0041] A method for covalently binding sulfur molecules to a double-bonded metal coordination polymer includes the following steps:

[0042] (1) Dissolve 0.79 g K2CO3 in 10 mL deionized water, add 100 mg BTA to the solution and stir continuously for 10 min, then add 0.02 g NaNO2 and stir continuously for 5 min. Continue stirring the mixture in a low-temperature (-5℃) reaction bath, while adding excess ACry (1 mL), and continue stirring at -5℃ for 3 h. Then transfer the reaction solution to room temperature and continue stirring for 24 h. Add the reaction mixture to 50 mL ethanol and filter out the precipitate. Slowly add the obtained clear filtrate to 100 mL diethyl ether solvent, seal and maintain at 4℃ for 48 h. Filter out the solid product precipitated in the diethyl ether solvent to obtain BTA-ACry.

[0043] (2) Dissolve 40 mg of the solid product (BTA-ACry) obtained in step (1) in 10 mL of deionized water. Add the solution dropwise to 10 mL of BC suspension with a solid content of 5 mg / mL and stir vigorously for 2 h. Add 10 mL of NiCl2·6H2O aqueous solution with a concentration of 8 mg / mL to the mixture and stir continuously for 2 h. Then slowly add 2 mL of concentrated ammonia (13.38 mol / L) to initiate the metal coordination polymerization reaction. After reacting overnight, wash the precipitate thoroughly and freeze-dry it to obtain BTA-ACry-Ni@BC aerogel.

[0044] (3) Add 2.5g of elemental sulfur and 50mg of BTA-ACry-Ni@BC aerogel to a 50mL reactor, ensuring that they do not come into contact with each other. After sealing the reactor, maintain the temperature at 250℃ for 12h. After cooling, the BTA-ACry-Ni@BC-S composite material covalently bonded to sulfur molecules is obtained.

[0045] Example 3

[0046] A method for covalently binding sulfur molecules to a double-bonded metal coordination polymer includes the following steps:

[0047] (1) Dissolve 0.79 g K2CO3 in 10 mL deionized water, add 100 mg BTA to the solution and stir continuously for 10 min, then add 0.02 g NaNO2 and stir continuously for 5 min. Continue stirring the mixture in a low-temperature (-5℃) reaction bath, while adding excess ACry (1 mL), and continue stirring at -5℃ for 3 h. Then transfer the reaction solution to room temperature and continue stirring for 24 h. Add the reaction mixture to 50 mL ethanol and filter out the precipitate. Slowly add the obtained clear filtrate to 100 mL diethyl ether solvent, seal and maintain at 4℃ for 48 h. Filter out the solid product precipitated in the diethyl ether solvent to obtain BTA-ACry.

[0048] (2) Dissolve 40 mg of the solid product (BTA-ACry) obtained in step (1) in 10 mL of deionized water. Add the solution dropwise to 10 mL of BC suspension with a solid content of 8 mg / mL and stir vigorously for 2 h. Add 10 mL of NiCl2·6H2O aqueous solution with a concentration of 5 mg / mL to the mixture and stir continuously for 2 h. Then slowly add 2 mL of concentrated ammonia (13.38 mol / L) to initiate the metal coordination polymerization reaction. After reacting overnight, wash the precipitate thoroughly and freeze-dry it to obtain BTA-ACry-Ni@BC aerogel.

[0049] (3) Add 2.5g of elemental sulfur and 50mg of BTA-ACry-Ni@BC aerogel to a 50mL reactor, ensuring that they do not come into contact with each other. After sealing the reactor, maintain the temperature at 190℃ for 12h. After cooling, the BTA-ACry-Ni@BC-S composite material covalently bonded to sulfur molecules is obtained.

[0050] Example 4

[0051] A method for covalently binding sulfur molecules to a double-bonded metal coordination polymer includes the following steps:

[0052] (1) Dissolve 0.79 g K2CO3 in 10 mL deionized water, add 100 mg BTA to the solution and stir continuously for 10 min, then add 0.02 g NaNO2 and stir continuously for 5 min. Continue stirring the mixture in a low-temperature (-5℃) reaction bath, while adding excess ACry (1 mL), and continue stirring at -5℃ for 3 h. Then transfer the reaction solution to room temperature and continue stirring for 24 h. Add the reaction mixture to 50 mL ethanol and filter out the precipitate. Slowly add the obtained clear filtrate to 100 mL diethyl ether solvent, seal and maintain at 4℃ for 48 h. Filter out the solid product precipitated in the diethyl ether solvent to obtain BTA-ACry.

[0053] (2) Dissolve 40 mg of the solid product (BTA-ACry) obtained in step (1) in 10 mL of deionized water. Add the solution dropwise to 10 mL of BC suspension with a solid content of 8 mg / mL and stir vigorously for 2 h. Add 10 mL of NiCl2·6H2O aqueous solution with a concentration of 5 mg / mL to the mixture and stir continuously for 2 h. Then slowly add 2 mL of concentrated ammonia (13.38 mol / L) to initiate the metal coordination polymerization reaction. After reacting overnight, wash the precipitate thoroughly and freeze-dry it to obtain BTA-ACry-Ni@BC aerogel.

[0054] (3) Add 2.5g of elemental sulfur and 50mg of BTA-ACry-Ni@BC aerogel to a 50mL reactor, ensuring that they do not come into contact with each other. After sealing the reactor, maintain the temperature at 150℃ for 12h. After cooling, the BTA-ACry-Ni@BC-S composite material covalently bonded to sulfur molecules is obtained.

[0055] Example 5

[0056] A method for covalently binding sulfur molecules to a double-bonded metal coordination polymer includes the following steps:

[0057] (1) Dissolve 0.79 g K2CO3 in 10 mL deionized water, add 100 mg BTA to the solution and stir continuously for 10 min, then add 0.02 g NaNO2 and stir continuously for 5 min. Continue stirring the mixture in a low-temperature (-5℃) reaction bath, while adding excess ACry (1 mL), and continue stirring at -5℃ for 3 h. Then transfer the reaction solution to room temperature and continue stirring for 24 h. Add the reaction mixture to 50 mL ethanol and filter out the precipitate. Slowly add the obtained clear filtrate to 100 mL diethyl ether solvent, seal and maintain at 4℃ for 48 h. Filter out the solid product precipitated in the diethyl ether solvent to obtain BTA-ACry.

[0058] (2) Dissolve 40 mg of the solid product (BTA-ACry) obtained in step (1) in 10 mL of deionized water. Add the solution dropwise to 10 mL of BC suspension with a solid content of 8 mg / mL and stir vigorously for 2 h. Add 10 mL of NiCl2·6H2O aqueous solution with a concentration of 2 mg / mL to the mixture and stir continuously for 2 h. Then slowly add 2 mL of concentrated ammonia (13.38 mol / L) to initiate the metal coordination polymerization reaction. After reacting overnight, wash the precipitate thoroughly and freeze-dry it to obtain BTA-ACry-Ni@BC aerogel.

[0059] (3) Add 2.5g of elemental sulfur and 50mg of BTA-ACry-Ni@BC aerogel to a 50mL reactor, ensuring that they do not come into contact with each other. After sealing the reactor, maintain the temperature at 190℃ for 12h. After cooling, the BTA-ACry-Ni@BC-S composite material covalently bonded to sulfur molecules is obtained.

[0060] Example 6

[0061] A method for covalently binding sulfur molecules to a double-bonded metal coordination polymer includes the following steps:

[0062] (1) Dissolve 0.79 g K2CO3 in 10 mL deionized water, add 100 mg BTA to the solution and stir continuously for 10 min, then add 0.02 g NaNO2 and stir continuously for 5 min. Continue stirring the mixture in a low-temperature (-5℃) reaction bath, while adding excess ACry (1 mL), and continue stirring at -5℃ for 3 h. Then transfer the reaction solution to room temperature and continue stirring for 24 h. Add the reaction mixture to 50 mL ethanol and filter out the precipitate. Slowly add the obtained clear filtrate to 100 mL diethyl ether solvent, seal and maintain at 4℃ for 48 h. Filter out the solid product precipitated in the diethyl ether solvent to obtain BTA-ACry.

[0063] (2) Dissolve 40 mg of the solid product (BTA-ACry) obtained in step (1) in 10 mL of deionized water. Add the solution dropwise to 10 mL of BC suspension with a solid content of 8 mg / mL and stir vigorously for 2 h. Add 10 mL of NiCl2·6H2O aqueous solution with a concentration of 8 mg / mL to the mixture and stir continuously for 2 h. Then slowly add 2 mL of concentrated ammonia (13.38 mol / L) to initiate the metal coordination polymerization reaction. After reacting overnight, wash the precipitate thoroughly and freeze-dry it to obtain BTA-ACry-Ni@BC aerogel.

[0064] (3) Add 2.5g of elemental sulfur and 50mg of BTA-ACry-Ni@BC aerogel to a 50mL reactor, ensuring that they do not come into contact with each other. After sealing the reactor, maintain the temperature at 190℃ for 12h. After cooling, the BTA-ACry-Ni@BC-S composite material covalently bonded to sulfur molecules is obtained.

[0065] Comparative Example 1

[0066] (1) Dissolve 40 mg BTA in 10 mL of deionized water. Add the solution dropwise to 10 mL of BC suspension with a solid content of 8 mg / mL and stir vigorously for 2 h. Add 10 mL of NiCl2·6H2O aqueous solution with a concentration of 5 mg / mL to the mixture and stir continuously for 2 h. Then slowly add 2 mL of concentrated ammonia (13.38 mol / L) to initiate the metal coordination polymerization reaction. After reacting overnight, wash the precipitate thoroughly and freeze-dry it to obtain BTA-Ni@BC aerogel.

[0067] (2) 2.5 g of elemental sulfur and 50 mg of BTA-Ni@BC aerogel were added simultaneously to a 50 mL reactor, ensuring that they did not come into contact with each other. After sealing the reactor, it was maintained at 190 °C for 12 h. After cooling, the BTA-Ni@BC-S composite material with non-covalent bonding to sulfur molecules was obtained.

[0068] Comparative Example 2

[0069] (1) Dissolve 0.79 g K2CO3 in 10 mL deionized water, add 100 mg BTA to the solution and stir continuously for 10 min, then add 0.02 g NaNO2 and stir continuously for 5 min. Continue stirring the mixture in a low-temperature (-5℃) reaction bath, while adding excess ACry (1 mL), and continue stirring at -5℃ for 3 h. Then transfer the reaction solution to room temperature and continue stirring for 24 h. Add the reaction mixture to 50 mL ethanol and filter out the precipitate. Slowly add the obtained clear filtrate to 100 mL diethyl ether solvent, seal and maintain at 4℃ for 48 h. Filter out the solid product precipitated in the diethyl ether solvent to obtain BTA-ACry.

[0070] (2) Dissolve 40 mg of the solid product (BTA-ACry) obtained in step (1) in 20 mL of deionized water. Add 10 mL of NiCl2·6H2O aqueous solution with a concentration of 5 mg / mL to the above solution. After stirring continuously for 2 h, slowly add 2 mL of concentrated ammonia (13.38 mol / L) to initiate the metal coordination polymerization reaction. After reacting overnight, wash the obtained precipitate thoroughly and freeze-dry it to obtain BTA-ACry-Ni aerogel.

[0071] Comparative Example 3

[0072] (1) Add 10 mL of BC suspension with a solid content of 8 mg / mL to 20 mL of deionized water and stir vigorously for 1 h. Freeze-dry the precipitate obtained after standing overnight to obtain BC aerogel.

[0073] (2) Add 2.5g of elemental sulfur and 50mg of BC aerogel to a 50mL reactor, ensuring that they do not come into contact with each other. After sealing the reactor, maintain the temperature at 190℃ for 12h. After cooling, the BC-S composite material with non-covalent bonding to sulfur molecules is obtained.

[0074] The composite materials prepared in Examples 1-6 and Comparative Examples 1-3 were applied to the positive electrode of a lithium-sulfur battery, including the following steps:

[0075] The composite materials obtained in Examples 1-6 and Comparative Examples 1-3, Super P, and PVDF were mixed at mass ratios of 60, 30, and 10 mg, respectively, and added to a weighing bottle. 2 mL of NMP solvent was added to the weighing bottle, and the mixture was stirred vigorously for 10 h. The resulting electrode slurry was coated onto conductive carbon cloth, and after vacuum drying, the carbon cloth electrode sheet was cut into circular pieces with a diameter of 12 mm. The total mass of electrode material on a single carbon cloth piece was 5.5 mg, of which the sulfur content was 1.5 mg. Finally, lithium metal was used as the negative electrode, Celgard 2250 was used as the separator, and the prepared carbon cloth positive electrode was assembled into a CR2032 coin cell.

[0076] The electrolyte used in the lithium-sulfur battery assembled with the above-mentioned cathode material was a solution of 1 mol / L LiTFSI and 1 wt% LiNO3 dissolved in a DOL-DME (1:1, v / v) mixed solvent. The battery assembly process was carried out in a glove box filled with Ar, and the assembled cells were CR2032 type coin cells. The cycle performance of this battery at a current density of 0.5 C and the test results of the lithium-ion diffusion coefficient obtained at different CV scan rates from 0.1 to 0.5 mV / s are shown in Table 1.

[0077] Table 1. Performance of the batteries assembled in Examples 1-6 and Comparative Examples 1-3 at a current density of 0.5 C and lithium-ion diffusion coefficients obtained at different CV scan rates.

[0078]

[0079] Table 1 shows that introducing an appropriate amount of double-bonded metal coordination polymer onto the surface of BC fibers and covalently binding sulfur molecules to it via vaporization at a suitable temperature has a significant impact on battery performance. A comparison of Examples 1, 3, and 5 reveals that the ratio of BC fibers to the metal coordination polymer has a significant influence on electrochemical performance. Specifically, when the proportion of the metal coordination polymer is low (Example 1), the lithium-sulfur battery exhibits very rapid degradation and a very low coulombic efficiency. + The ion diffusion capability is relatively limited. This is mainly because there are very few metallic Ni and amino groups from the metal coordination polymer in this case, resulting in a severe lack of control and catalytic conversion ability for polysulfides, leading to a serious polysulfide shuttle effect. Furthermore, the lack of amino groups is also detrimental to the rapid conduction of lithium ions. A comparison between Example 2 and Example 3 shows that excessively high heat treatment temperatures negatively impact the performance of the lithium-sulfur battery. This is mainly because excessively high heat treatment temperatures cause partial decomposition of the BC fiber framework, thus weakening the structural stability of the electrode material and primarily affecting cycle stability. A comparison between Example 4 and Example 3 shows that excessively low heat treatment temperatures severely affect the performance of the lithium-sulfur battery. This is mainly because excessively low heat treatment temperatures cannot guarantee the formation of covalent bonds between the double bonds and sulfur molecules. The non-covalently bonded active material sulfur is prone to shuttle effects during charge / discharge, therefore Example 4 exhibits severe cycle decay and low coulombic efficiency. The electrochemical performance of Example 6 is relatively good and close to that of Example 3. Compared to Example 3, Example 6 provides a more sufficient amount of Ni. 2+ Induced coordination polymerization reaction, the remaining Ni 2+ It can be cleaned during the washing process after the reaction.

[0080] In Comparative Example 1, BTA-Ni@BC aerogel without double bond modification was used for vapor deposition of sulfur molecules. Due to the lack of double bond modification, covalently linked active sulfur could not be formed, resulting in extremely low battery efficiency, severe degradation, and low Li... + The diffusion coefficient is not high. In Comparative Example 2, BTA-ACry-Ni aerogel without a BC framework was used for vapor deposition of active sulfur. However, without the support of the BC framework, the micro / nano structure of the BTA-ACry-Ni aerogel is very dense, which will severely hinder the diffusion of Li. + Migration, therefore, the Li in the comparative example 2 sample + The diffusion coefficient is very small. In Comparative Example 3, sulfur, an active material for aerogel vapor deposition containing only BC, was selected. Since pure BC cannot be covalently bonded to sulfur molecules and its control over polysulfides is very limited, the degradation of the sample in Comparative Example 3 is very severe, and the average coulombic efficiency and Li+ diffusion coefficient are both small.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for covalently binding sulfur molecules to a double-bonded metal coordination polymer, characterized in that: Includes the following steps: 1) Dissolve tetraaminobenzene in an aqueous solution containing potassium carbonate and sodium nitrite, add acryloyl chloride under low temperature conditions, filter, and obtain BTA-ACry; 2) Dissolve the BTA-ACry obtained in step 1) in water, add bacterial cellulose suspension dropwise and stir to mix, then add nickel chloride hexahydrate aqueous solution, stir and add concentrated ammonia water dropwise to initiate coordination polymerization, wash and freeze dry to obtain BTA-ACry-Ni@BC aerogel. 3) Elemental sulfur and the BTA-ACry-Ni@BC aerogel obtained in step 2) are placed in a reaction vessel without contact between them and reacted at high temperature to obtain the BTA-ACry-Ni@BC-S composite material.

2. The method for covalently binding sulfur molecules to a double-bonded metal coordination polymer according to claim 1, characterized in that: In step 1), the low temperature condition is -5℃.

3. The method for covalently binding sulfur molecules to a double-bonded metal coordination polymer according to claim 1, characterized in that: In step 2), the solid content of the bacterial cellulose suspension is 5-10 mg / mL.

4. The method for covalently binding sulfur molecules to a double-bonded metal coordination polymer according to claim 1, characterized in that: In step 2), the concentration of the nickel chloride hexahydrate aqueous solution is 2-8 mg / mL.

5. The method for covalently binding sulfur molecules to a double-bonded metal coordination polymer according to claim 1, characterized in that: In step 3), the high-temperature reaction temperature is 150-250℃.

6. The composite material of metal coordination polymer covalently bonded to sulfur molecules prepared by the method of covalently bonding sulfur molecules to double-bonded metal coordination polymers according to any one of claims 1 to 5.

7. The application of the metal coordination polymer covalently bonded sulfur molecule composite material according to claim 6 in the positive electrode of lithium-sulfur battery.

8. The application of the metal coordination polymer covalently bonded sulfur molecule composite material according to claim 7 in the positive electrode of a lithium-sulfur battery, characterized in that, The process includes the following steps: mixing a composite material of metal coordination polymer covalently bonded to sulfur molecules, SuperP, and PVDF, then adding NMP solvent and stirring; coating the prepared electrode slurry onto conductive carbon cloth, drying it under vacuum, and then cutting the carbon cloth electrode sheet into a circular piece; finally, using lithium metal as the negative electrode and Celgard 2250 as the separator, assembling it together with the prepared carbon cloth positive electrode into a CR2032 coin cell.

9. The application of the metal coordination polymer covalently bonded sulfur molecule composite material according to claim 8 in the positive electrode of a lithium-sulfur battery, characterized in that: The mass ratio of the composite material containing metal coordination polymer covalently bonded to sulfur molecules, Super P, and PVDF is 6:3:

1.

10. The application of the metal-coordinated polymer covalently bonded sulfur molecule composite material according to claim 7 in the positive electrode of a lithium-sulfur battery, characterized in that: The initial discharge specific capacity is 1208~1325 mAh / g; the specific capacity after 100 discharges is 821~969 mAh / g; the specific capacity after 500 discharges is 589~796 ​​mAh / g; the average coulombic efficiency is 95.8~99.2%; Li + The diffusion coefficient is 6.36 × 10⁻⁶. -5 ~1.22×10 -4 cm 2 / s.

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