Sulfur storage material, lithium-sulfur battery positive electrode material and preparation method thereof, and lithium-sulfur battery

Abstract

The present invention discloses a sulfur storage material, a lithium-sulfur battery positive electrode material, a preparation method and a lithium-sulfur battery, wherein the sulfur storage material comprises a hollow carbon sphere doped with non-metallic atoms and an Fe-containing X vacancy embedded in the surface of the hollow carbon sphere. a X b / Mn c X d Heterojunction nanoparticles; X is Se, S or N; wherein, when X is Se, a=b=c=d=1; when X is S, a=2, b=3, c=d=1; when X is N, a=3, b=c=d=1. In the present invention, the doping of non-metallic atoms can provide more polar sites for chemical adsorption of polysulfides to inhibit the shuttling of polysulfides, Fe a X b / Mn c X d Heterojunctions and X vacancies can regulate the electronic structure distribution within the material, increasing the material's electronic conductivity, improving catalytic performance, lowering the energy barrier for polysulfide redox reactions, and enhancing the performance of lithium-sulfur batteries. The hollow sphere structure can withstand changes in sulfur volume during charge and discharge. Lithium-sulfur batteries prepared using the sulfur storage material provided by this invention exhibit excellent charge-discharge performance and a long cycle life.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur batteries, and in particular to a sulfur storage material, a lithium-sulfur battery positive electrode material and a preparation method thereof, and a lithium-sulfur battery. Background Art

[0002] Lithium-sulfur batteries are expected to become the next generation of commercial batteries due to their abundant natural sulfur resources, high specific capacity (1675mAh / g) and specific energy (2600Wh / kg), environmental friendliness, and low cost. However, the current research and development of lithium-sulfur batteries are hindered by the following reasons: (1) poor conductivity of elemental sulfur; (2) during the charge and discharge process, lithium polysulfide shuttles from the positive electrode through the separator to the lithium negative electrode side and reacts with it to form non-conductive inert Li2S attached to the surface of the lithium negative electrode, resulting in increased polarization of the lithium negative electrode and continuous consumption of the positive electrode active material sulfur; (3) during the charge and discharge process, the active material sulfur undergoes a large volume change, resulting in irreversible damage to the structure of the positive electrode material; and (4) the slow sulfur redox reaction kinetics during the charge and discharge process. Overcoming the above problems is a necessary condition for the commercialization of lithium-sulfur batteries.

[0003] The currently available single carbon-based sulfur storage materials, metal and non-metallic sulfur storage materials, heterojunction, defect and other interface engineering sulfur storage materials cannot overcome the above difficulties at the same time.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a sulfur storage material, a lithium-sulfur battery positive electrode material, a preparation method, and a lithium-sulfur battery, aiming to solve the problem that lithium-sulfur batteries prepared from existing sulfur storage materials cannot simultaneously achieve high positive electrode conductivity and small volume change, small negative electrode polarization, and faster redox reaction kinetics.

[0006] The technical solutions of the present invention are as follows:

[0007] In a first aspect of the present invention, a sulfur storage material is provided, wherein the sulfur storage material comprises hollow carbon spheres doped with non-metal atoms and Fe containing X vacancies embedded in the surface of the hollow carbon spheres. a X b / Mn c X d Heterojunction nanoparticles; X is Se, S or N;

[0008] Wherein, when X is Se, a=b=c=d=1;

[0009] When X is S, a=2, b=3, c=d=1;

[0010] When X is N, a=3, b=c=d=1.

[0011] Optionally, the non-metal atom is selected from at least one of N, B, and P.

[0012] Optionally, the non-metal atom is selected from N and B.

[0013] A second aspect of the present invention provides a method for preparing the sulfur storage material as described above, comprising the steps of:

[0014] Adding iron salt, manganese salt, trimesic acid, organic polymer, and ionic liquid containing non-metallic elements into a solvent to obtain a mixed solution;

[0015] reacting the mixed solution at a first preset temperature for a first preset time to obtain a first precursor;

[0016] calcining the first precursor at a second preset temperature for a second preset time under a hydrogen atmosphere to obtain a second precursor;

[0017] The sulfur storage material is obtained by selenizing, sulfurizing or nitriding the second precursor at a third preset temperature for a third preset time.

[0018] Optionally, the mass ratio of the iron salt, manganese salt, trimesic acid, organic polymer, and ionic liquid containing non-metallic elements is (0.6-1):(0.2-0.4):(0.2-1):(1-3):(0.4-0.6).

[0019] Optionally, the iron salt is selected from at least one of ferric chloride, ferric nitrate, and ferric sulfate;

[0020] And / or, the manganese salt is at least one selected from manganese nitrate, manganese chloride, and manganese sulfate;

[0021] and / or, the organic polymer is selected from at least one of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and polypropylene glycol;

[0022] And / or, the ionic liquid containing a non-metallic element is selected from at least one of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate;

[0023] And / or, the solvent is selected from at least one of water, ethanol, ethylene glycol, and N,N-dimethylformamide.

[0024] Optionally, the first preset temperature is 80-160° C., and the first preset time is 8-15 hours;

[0025] And / or, the second preset temperature is 500-1000° C., and the second preset time is 2-8 hours;

[0026] And / or, the third preset temperature is 300-800° C., and the third preset time is 2-6 hours.

[0027] A third aspect of the present invention provides a method for preparing a positive electrode material for a lithium-sulfur battery, comprising the steps of:

[0028] The sublimated sulfur is mixed with the sulfur storage material of the present invention and heated under sealed conditions to obtain the lithium-sulfur battery positive electrode material.

[0029] In a fourth aspect of the present invention, a positive electrode material for a lithium-sulfur battery is provided, wherein the positive electrode material is prepared by the method for preparing the positive electrode material for a lithium-sulfur battery as described above.

[0030] In a fifth aspect of the present invention, a lithium-sulfur battery is provided, comprising a positive electrode sheet, wherein the material of the positive electrode sheet comprises the lithium-sulfur battery positive electrode material of the present invention as described above.

[0031] Beneficial effect: The sulfur storage material of the present invention comprises hollow carbon spheres doped with non-metal atoms and Fe containing X vacancies (Se vacancies, S vacancies or N vacancies) embedded in the surface of the hollow carbon spheres. a X b / Mn c X d Heterojunction nanoparticles. Among them, the doping of non-metallic atoms can provide more polar sites for chemical adsorption of polysulfides, thereby inhibiting the shuttle of polysulfides, effectively avoiding the increase of negative electrode polarization caused by the shuttle of polysulfides to the negative electrode side; Fe a X b / Mn c X d Heterojunctions and X vacancies (Se vacancies, S vacancies, or N vacancies) can regulate the electronic structure distribution inside the material, increase the electronic conductivity of the material, improve catalytic performance, reduce the energy barrier of polysulfide redox reactions, and improve the performance of lithium-sulfur batteries; the hollow sphere structure can accommodate more sulfur, withstand the change in sulfur volume during charge and discharge, and avoid damage to the electrode material structure due to the change in sulfur volume. In addition, during the discharge process, polysulfides are preferentially adsorbed on Fe a X b / Mn c X dAt the heterojunction boundary, a vertical Li2S deposition layer is formed in a 3D pattern, effectively preventing surface passivation and providing sufficient active sites and channels for subsequent, continuous Li2S nucleation and deposition. Lithium-sulfur batteries fabricated using the sulfur storage material provided by this invention exhibit advantages such as high positive electrode conductivity and minimal volume change, minimal negative electrode polarization and rapid redox reaction kinetics, excellent charge-discharge performance, and a long cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the SEM image of FeSe / MnSe / NBC in Example 1 of the present invention.

[0033] Figure 2 1 is the element distribution diagram of FeSe / MnSe / NBC in Example 1 of the present invention.

[0034] Figure 3 This is the TEM image of FeSe / MnSe / NBC in Example 1 of the present invention.

[0035] Figure 4 This is the XRD pattern of FeSe / MnSe / NBC in Example 1 of the present invention.

[0036] Figure 5 Graphs showing the EPR response results of FeSe / MnSe / NBC in Example 1 of the present invention, FeSe / C in Comparative Example 1, and MnSe / C in Comparative Example 2.

[0037] Figure 6 This is a graph showing the charge and discharge test results of S / FeSe / MnSe / NBC in Example 5 of the present invention.

[0038] Figure 7 This is a graph showing the cycle test results of S / FeSe / MnSe / NBC in Example 5 of the present invention.

[0039] Figure 8 This is a graph showing the charge and discharge test results of S / FeSe / C in Comparative Example 3 of the present invention.

[0040] Figure 9 This is a graph showing the cycle test results of S / FeSe / C in Comparative Example 3 of the present invention.

[0041] Figure 10 Schematic diagram of the deposition process of polysulfides on the surface of S / FeSe / MnSe / NBC in Example 5 of the present invention and S / FeSe / C in Comparative Example 3 during discharge. DETAILED DESCRIPTION

[0042] The present invention provides a sulfur storage material, a lithium-sulfur battery cathode material, a preparation method, and a lithium-sulfur battery. To clarify the objectives, technical solutions, and advantages of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0043] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0044] The embodiment of the present invention provides a sulfur storage material, wherein the sulfur storage material comprises a hollow carbon sphere doped with a non-metal atom and a Fe containing X vacancies embedded in the surface of the hollow carbon sphere. a X b / Mn c X d Heterojunction nanoparticles; X is Se, S or N;

[0045] Wherein, when X is Se, a=b=c=d=1;

[0046] When X is S, a=2, b=3, c=d=1;

[0047] When X is N, a=3, b=c=d=1.

[0048] In this embodiment, embedded in the surface of the hollow carbon sphere may be FeSe / MnSe heterojunction nanoparticles containing Se vacancies, Fe2S3 / MnS heterojunction nanoparticles containing S vacancies, or Fe3N / MnN heterojunction nanoparticles containing N vacancies.

[0049] In this embodiment, the sulfur storage material includes hollow carbon spheres doped with non-metal atoms and Fe containing X vacancies (Se vacancies, S vacancies or N vacancies) embedded in the surface of the hollow carbon spheres. a X b / Mn c X d Heterojunction nanoparticles.

[0050] Among them, the doping of non-metallic atoms can provide more polar sites for chemical adsorption of polysulfides, enhance the chemical adsorption capacity of polysulfides, thereby inhibiting the shuttling of polysulfides and effectively avoiding the increase of negative electrode polarization caused by the shuttling of polysulfides to the negative electrode side.

[0051] Fe a X b / Mn c X dHeterojunctions (FeSe / MnSe heterojunctions, Fe2S3 / MnS heterojunctions or Fe3N / MnN heterojunctions) can regulate the electronic structure distribution inside the material, increase the electronic conductivity of the material, improve the catalytic performance, reduce the energy barrier of the polysulfide redox reaction, improve the reaction kinetics, and improve the performance of lithium-sulfur batteries. In addition, during the discharge process, polysulfides are preferentially adsorbed on Fe a X b / Mn c X d At the heterojunction boundary, a vertical Li2S deposition layer is generated in a 3D pattern, which effectively avoids the passivation of the material surface and provides sufficient active sites and channels for the subsequent continuous Li2S nucleation and deposition. a X b / Mn c X d The heterojunction boundary preferentially adsorbs polysulfides, which causes the Li2S deposition layer to preferentially nucleate and grow in a 3D pattern at and perpendicular to the boundary, providing sufficient active sites and channels for the subsequent redox reaction of polysulfides. Figure 10 shown.

[0052] X vacancies (Se vacancies, S vacancies or N vacancies) can regulate Fe a X b / Mn c X d The coordination environment and electronic structure of heterojunction atoms further improve the conductivity of the material and promote the redox reaction of polysulfides.

[0053] The hollow sphere structure can accommodate more sulfur, withstand the volume changes of sulfur during charging and discharging, and avoid irreversible damage to the electrode material structure caused by the volume changes of sulfur during charging and discharging.

[0054] The sulfur storage material provided in this embodiment integrates non-metallic atom doping, heterojunction, defect interface engineering, and a unique hollow geometric structure. Compared with the current single-function sulfur storage materials, it has a very good electrochemical effect, can provide abundant surface active sites, enhance the chemical adsorption capacity of polysulfides, effectively inhibit the polysulfide shuttle effect, reduce the energy barrier of polysulfide redox reaction, improve reaction kinetics, and alleviate the irreversible damage to the electrode material structure caused by sulfur volume change during charging and discharging. It can simultaneously solve many problems existing in lithium-sulfur batteries. The lithium-sulfur battery prepared using the sulfur storage material provided by the present invention has the advantages of good charge and discharge performance and long cycle life.

[0055] In one embodiment, the non-metallic atom is selected from at least one of N, B, and P. Doping with heteroatoms such as nitrogen, boron, and phosphorus can provide abundant polar sites on the surface of the non-polar carbon-based material, thereby enhancing the chemical adsorption capacity for polysulfides and inhibiting the shuttling effect of polysulfides, thereby achieving stable cycling performance of lithium-sulfur batteries.

[0056] In a further embodiment, the non-metal atom is selected from N and B.

[0057] In one embodiment, the diameter of the hollow carbon sphere is 400-600 nm.

[0058] An embodiment of the present invention further provides a method for preparing the sulfur storage material of the present invention, which comprises the steps of:

[0059] S1. Adding iron salt, manganese salt, trimesic acid, organic polymer, and ionic liquid containing non-metallic elements to a solvent to obtain a mixed solution;

[0060] S2, reacting the mixed solution at a first preset temperature for a first preset time to obtain a first precursor;

[0061] S3. calcining the first precursor at a second preset temperature for a second preset time under a hydrogen atmosphere to obtain a second precursor;

[0062] S4. Selenide, sulfurize or nitride the second precursor at a third preset temperature for a third preset time to obtain the sulfur storage material.

[0063] The preparation method provided in this embodiment is simple. Non-metallic atoms can be introduced by using an ionic liquid containing non-metallic elements as a dopant. Hollow carbon spheres doped with non-metallic atoms and Fe-containing X vacancies embedded on the surface of the hollow carbon spheres can be successfully prepared through hydrothermal synthesis and subsequent selenization, sulfidation or nitridation. a X b / Mn c X d Preparation of heterojunction nanoparticle sulfur storage materials.

[0064] In step S1, in one embodiment, the mass ratio of the iron salt, manganese salt, trimesic acid, organic polymer, and ionic liquid containing non-metallic elements is (0.6-1): (0.2-0.4): (0.2-1): (1-3): (0.4-0.6). In this embodiment, the iron salt, manganese salt, trimesic acid, organic polymer, and ionic liquid containing non-metallic elements are used as iron source, manganese source, ligand in the reaction process, carbon source, and non-metallic element source dopant, respectively, to achieve the preparation of hollow carbon spheres doped with non-metallic atoms, and make Fe containing X vacancies a X b / Mnc X d Heterojunction nanoparticles are embedded in the surface of the hollow carbon spheres.

[0065] In one embodiment, the iron salt is selected from at least one of ferric chloride, ferric nitrate, and ferric sulfate, but is not limited thereto.

[0066] In one embodiment, the manganese salt is selected from at least one of manganese nitrate, manganese chloride, and manganese sulfate, but is not limited thereto.

[0067] In one embodiment, the organic polymer is selected from at least one of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polypropylene glycol (PPG), but is not limited thereto. Specifically, the PVP can be subdivided into K15, K25, K30, K60, K80, or K90 according to molecular weight.

[0068] In one embodiment, the ionic liquid containing non-metallic elements is selected from at least one of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate, but is not limited thereto. For example, when the ionic liquid containing non-metallic elements is selected from 1-butyl-3-methylimidazolium tetrafluoroborate, nitrogen and boron heteroatoms can be doped. When the ionic liquid containing non-metallic elements is selected from 1-butyl-3-methylimidazolium hexafluorophosphate, nitrogen and phosphorus heteroatoms can be doped. When the ionic liquid containing non-metallic elements is selected from 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate, nitrogen, boron, and phosphorus heteroatoms can be doped.

[0069] In one embodiment, the solvent is selected from at least one of water, ethanol, ethylene glycol, and N,N-dimethylformamide.

[0070] In step S2, the mixed solution is subjected to a hydrothermal reaction at a first preset temperature.

[0071] In one embodiment, the first preset temperature is 80-160°C, and the first preset time is 8-15 hours. For example, the first preset temperature may be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or 160°C; and the first preset time may be 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, or 15 hours.

[0072] In step S3, in one embodiment, the second preset temperature is 500-1000°C, and the second preset time is 2-8 hours. For example, the second preset temperature may be 500°C, 600°C, 700°C, 800°C, 900°C, or 1000°C; and the second preset time may be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours.

[0073] In step S4, in one embodiment, the third preset temperature is 300-800°C, and the third preset time is 2-6 hours. For example, the third preset temperature can be 300°C, 400°C, 500°C, 600°C, 700°C, or 800°C; and the third preset time can be 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0074] In one embodiment, the step of obtaining the sulfur storage material after selenizing the second precursor at a third preset temperature for a third preset time specifically includes placing the second precursor and selenium powder in a tube furnace downstream and upstream of a gas inlet direction, respectively, introducing a mixture of argon and hydrogen, and calcining at a temperature of 300 to 800° C. for 2 to 6 hours to obtain the sulfur storage material. In this embodiment, the presence of hydrogen in the mixed gas ensures the formation of a high content of Se vacancies, resulting in a FeSe / MnSe heterojunction rich in Se vacancies. The high content of Se vacancies can regulate the coordination environment and electronic structure of the atoms in the FeSe / MnSe heterojunction, thereby further improving the conductivity of the material and promoting the redox reaction of polysulfides.

[0075] In one embodiment, the mass ratio of the second precursor to the selenium powder is 1:(0.5-4).

[0076] In one embodiment, the step of obtaining the sulfur storage material after sulfurizing the second precursor at a third preset temperature for a third preset time specifically includes placing the second precursor and sulfur in a tube furnace downstream and upstream of a gas inlet direction, respectively, introducing a mixture of argon and hydrogen, and calcining at a temperature of 300 to 800° C. for 2 to 6 hours to obtain the sulfur storage material. In this embodiment, the presence of hydrogen in the mixed gas ensures the formation of a high content of Se vacancies, resulting in an Fe2S3 / MnS heterojunction rich in S vacancies. The high content of S vacancies can regulate the coordination environment and electronic structure of the atoms in the Fe2S3 / MnS heterojunction, thereby further improving the conductivity of the material and promoting the redox reaction of polysulfides.

[0077] In one embodiment, the mass ratio of the second precursor to the sulfur is 1:(0.5-4).

[0078] In one embodiment, the step of obtaining the sulfur storage material after nitriding the second precursor at a third preset temperature for a third preset time specifically includes placing the second precursor in a tube furnace, introducing ammonia gas and a mixture of argon and hydrogen, and calcining at a temperature of 300-800°C for 2-6 hours to obtain the sulfur storage material. In this embodiment, the presence of hydrogen in the mixture ensures the formation of a high content of N vacancies, resulting in a Fe3N / MnN heterojunction rich in N vacancies. The high content of N vacancies can regulate the coordination environment and electronic structure of the atoms in the Fe3N / MnN heterojunction, thereby further improving the conductivity of the material and promoting the redox reaction of polysulfides.

[0079] The present invention also provides a method for preparing a positive electrode material for a lithium-sulfur battery, which comprises the following steps:

[0080] The sublimated sulfur is mixed with the sulfur storage material of the present invention and heated under sealed conditions to obtain the lithium-sulfur battery positive electrode material.

[0081] In one embodiment, the mass ratio of the sublimated sulfur to the sulfur storage material is (6-9):1.

[0082] In one embodiment, the heating temperature is 140-180° C. and the heating time is 10-15 hours. At this temperature, the molten sulfur will penetrate into the interior of the sulfur storage material to form a positive electrode material for a lithium-sulfur battery.

[0083] The present invention also provides a lithium-sulfur battery cathode material, which is prepared using the lithium-sulfur battery cathode material described above in the present invention. Specifically, the lithium-sulfur battery cathode material includes a sulfur storage material and sulfur stored in the sulfur storage material.

[0084] An embodiment of the present invention further provides a lithium-sulfur battery, including a positive electrode sheet, wherein the material of the positive electrode sheet includes the lithium-sulfur battery positive electrode material described above. In this embodiment, the lithium-sulfur battery has the advantages of good positive electrode conductivity and small volume change, small negative electrode polarization and fast redox reaction kinetics, as well as good charge and discharge performance and a long cycle life.

[0085] The following describes it in detail through specific examples.

[0086] Example 1

[0087] Preparation of sulfur storage materials:

[0088] 810 mg of FeCl3·6H2O, 358 mg of Mn(NO3)2, 420 mg of trimesic acid (H3BTC), 2.0 g of PVP(K30) and 500 mg of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) were added to 80 mL of N,N-dimethylformamide (DMF), stirred and dissolved for 3 hours to obtain a mixed solution;

[0089] The mixed solution was transferred to a hydrothermal kettle and sealed, and then transferred to an oven and heated at 150°C for 12 hours. After naturally cooling to room temperature, the precipitate was filtered to obtain a precipitate. The precipitate was washed three times with DMF and anhydrous ethanol, respectively, and then transferred to an oven and dried at 120°C for 6 hours. The dried precipitate was then taken out and placed in a tube furnace. It was calcined at 800°C for 5 hours under a hydrogen atmosphere and then taken out after naturally cooling to room temperature. The obtained product was recorded as Fe3C / MnO / NBC.

[0090] Fe3C / MnO / NBC and selenium powder were placed in two porcelain boats in a mass ratio of 1:2. The porcelain boat containing selenium powder was placed upstream of the gas inlet direction of the tube furnace, and the porcelain boat containing Fe3C / MnO / NBC was placed downstream of the gas inlet direction of the tube furnace. Then, a mixture of argon and hydrogen was introduced, and the mixture was calcined at 500°C for 3 hours. After naturally cooling to room temperature, a sulfur storage material was obtained, which was recorded as: FeSe / MnSe / NBC.

[0091] Example 2

[0092] Preparation of sulfur storage materials:

[0093] 810 mg of FeCl3·6H2O, 252 mg of MnCl2, 420 mg of trimesic acid (H3BTC), 2.0 g of PVP (K15), and 500 mg of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) were added to 80 mL of N,N-dimethylformamide (DMF), stirred and dissolved for 3 hours to obtain a mixed solution;

[0094] The mixed solution was transferred to a hydrothermal kettle and sealed, and then transferred to an oven and heated at 150°C for 12 hours. After naturally cooling to room temperature, the precipitate was filtered to obtain a precipitate. The precipitate was washed three times with DMF and anhydrous ethanol, respectively, and then transferred to an oven and dried at 120°C for 6 hours. The dried precipitate was then taken out and placed in a tube furnace. It was calcined at 800°C for 5 hours under a hydrogen atmosphere and then taken out after naturally cooling to room temperature. The obtained product was recorded as Fe3C / MnO / NBC.

[0095] Fe3C / MnO / NBC and selenium powder were placed in two porcelain boats in a mass ratio of 1:2. The porcelain boat containing selenium powder was placed upstream of the gas inlet direction of the tube furnace, and the porcelain boat containing Fe3C / MnO / NBC was placed downstream of the gas inlet direction of the tube furnace. Then, a mixture of argon and hydrogen was introduced, and the mixture was calcined at 800°C for 3 hours. After naturally cooling to room temperature, a sulfur storage material was obtained, which was recorded as: FeSe / MnSe / NBC-1.

[0096] Example 3

[0097] Preparation of sulfur storage materials:

[0098] 726 mg of Fe(NO3)3·9H2O, 252 mg of MnCl2, 420 mg of trimesic acid (H3BTC), 2.0 g of PVP (K88-96) and 500 mg of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) were added to 80 mL of N,N-dimethylformamide (DMF), stirred and dissolved for 3 hours to obtain a mixed solution;

[0099] The mixed solution was transferred to a hydrothermal kettle and sealed, and then transferred to an oven and heated at 150°C for 12 hours. After naturally cooling to room temperature, the precipitate was filtered to obtain a precipitate. The precipitate was washed three times with DMF and anhydrous ethanol, respectively, and then transferred to an oven and dried at 120°C for 6 hours. The dried precipitate was then taken out and placed in a tube furnace. It was calcined at 800°C for 5 hours under a hydrogen atmosphere and then taken out after naturally cooling to room temperature. The obtained product was recorded as Fe3C / MnO / NBC.

[0100] Fe3C / MnO / NBC and selenium powder were placed in two porcelain boats in a mass ratio of 1:2. The porcelain boat containing selenium powder was placed upstream of the gas inlet direction of the tubular furnace, and the porcelain boat containing Fe3C / MnO / NBC was placed downstream of the gas inlet direction of the tubular furnace. Then, a mixture of argon and hydrogen was introduced, and the mixture was calcined at 800°C for 3 hours. After naturally cooling to room temperature, a sulfur storage material was obtained, which was recorded as: FeSe / MnSe / NBC-2.

[0101] Example 4

[0102] Preparation of sulfur storage materials:

[0103] 726 mg of Fe(NO3)3·9H2O, 252 mg of MnCl2, 1 g of trimesic acid (H3BTC), 2.0 g of PVP(K60), and 500 mg of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) were added to 80 mL of N,N-dimethylformamide (DMF), stirred and dissolved for 3 hours to obtain a mixed solution;

[0104] The mixed solution was transferred to a hydrothermal kettle and sealed, and then transferred to an oven and heated at 150°C for 12 hours. After naturally cooling to room temperature, the precipitate was filtered to obtain a precipitate. The precipitate was washed three times with DMF and anhydrous ethanol, respectively, and then transferred to an oven and dried at 120°C for 6 hours. The dried precipitate was then taken out and placed in a tube furnace. It was calcined at 800°C for 5 hours under a hydrogen atmosphere and then taken out after naturally cooling to room temperature. The obtained product was recorded as Fe3C / MnO / NBC.

[0105] Fe3C / MnO / NBC and selenium powder were placed in two porcelain boats in a mass ratio of 1:2. The porcelain boat containing selenium powder was placed upstream of the gas inlet direction of the tube furnace, and the porcelain boat containing Fe3C / MnO / NBC was placed downstream of the gas inlet direction of the tube furnace. Then, a mixture of argon and hydrogen was introduced, and the mixture was calcined at 800°C for 3 hours. After naturally cooling to room temperature, a sulfur storage material was obtained, which was recorded as: FeSe / MnSe / NBC-3.

[0106] Example 5

[0107] Preparation of lithium-sulfur battery positive electrode materials:

[0108] The sublimed sulfur and the FeSe-MnSe / NBC prepared in Example 1 were fully ground at a mass ratio of 8:1 for 2 h, and then transferred to a glove box (argon atmosphere). In the glove box, it was encapsulated in a hydrothermal kettle, and then taken out and placed in an oven. It was heated at 155 ° C for 12 h and naturally cooled to room temperature to obtain a lithium-sulfur battery positive electrode material, recorded as S / FeSe / MnSe / NBC.

[0109] Comparative Example 1

[0110] Preparation of sulfur storage materials:

[0111] 810 mg of FeCl3·6H2O, 210 mg of trimesic acid (H3BTC), and 1.0 g of PVP (K30) were added to 80 mL of N,N-dimethylformamide (DMF), and the mixture was stirred and dissolved for 3 hours to obtain a mixed solution;

[0112] The above solution was transferred to a hydrothermal kettle and sealed, then transferred to an oven and heated at 150°C for 12h. After cooling naturally to room temperature, the precipitate was filtered to obtain a precipitate, washed three times with DMF and anhydrous ethanol respectively, and then transferred to an oven at 120°C for 6 hours. The dried precipitate was then taken out, placed in a tube furnace, and calcined at 800°C for 5 hours under a hydrogen atmosphere. After cooling naturally to room temperature, it was taken out. The intermediate product and selenium powder after the above removal were weighed in a mass ratio of 1:2 and placed in two porcelain boats respectively. The porcelain boat containing selenium powder was placed upstream of the gas inlet direction in the tube furnace, and the porcelain boat containing the intermediate product was placed downstream of the gas inlet direction in the tube furnace. Then argon was passed and calcined at 500°C for 3h. After cooling naturally to room temperature, a sulfur storage material was obtained, which was recorded as FeSe / C (which is a hollow carbon sphere material with FeSe nanoparticles embedded on the surface).

[0113] Comparative Example 2

[0114] Preparation of sulfur storage materials:

[0115] 358 mg of Mn(NO3)2, 210 mg of trimesic acid (H3BTC), and 1.0 g of PVP (K30) were added to 80 mL of N,N-dimethylformamide (DMF), stirred and dissolved for 3 hours to obtain a mixed solution;

[0116] The mixed solution was transferred to a hydrothermal kettle and sealed, and then transferred to an oven and heated at 150°C for 12 hours. After naturally cooling to room temperature, the precipitate was filtered to obtain the precipitate. The precipitate was washed three times with DMF and anhydrous ethanol respectively, and then transferred to an oven and dried at 120°C for 6 hours. The dried precipitate was then taken out and placed in a tubular furnace. In a hydrogen atmosphere, it was calcined at 800°C for 5 hours. After naturally cooling to room temperature, it was taken out and the above-mentioned product and selenium powder were placed in two porcelain boats in a mass ratio of 1:2. The porcelain boat containing selenium powder was placed upstream of the gas inlet direction of the tubular furnace, and the porcelain boat containing the intermediate product was placed downstream of the gas inlet direction of the tubular furnace. Then, a mixture of argon and hydrogen was introduced, and the mixture was calcined at 500°C for 3 hours. After naturally cooling to room temperature, a sulfur storage material was obtained, which was recorded as MnSe / C.

[0117] Comparative Example 3

[0118] Preparation of lithium-sulfur battery positive electrode materials:

[0119] The sublimed sulfur and the FeSe / C prepared in Comparative Example 1 were fully ground at a mass ratio of 8:1 for 2 h, and then transferred to a glove box (argon atmosphere). In the glove box, they were encapsulated in a hydrothermal kettle, and then taken out and placed in an oven. They were heated at 155 ° C for 12 h and naturally cooled to room temperature to obtain a lithium-sulfur battery positive electrode material, recorded as S / FeSe / C.

[0120] test:

[0121] 1. The FeSe / MnSe / NBC in Example 1 was subjected to SEM test, element distribution test, TEM test and XRD test respectively.

[0122] (1) SEM images of FeSe / MnSe / NBC Figure 1 As shown, it can be seen that FeSe / MnSe / NBC has a regular hollow spherical structure with a diameter of about 500 nm.

[0123] (2) The element distribution diagram of FeSe / MnSe / NBC is as follows Figure 2 As shown, the uniform distribution of C, Se, Mn, Fe, B and N elements can be seen from the figure, confirming the successful doping of N and B elements.

[0124] (3) TEM images of FeSe / MnSe / NBC Figure 3 As shown, from Figure 3 The existence of FeSe / MnSe heterojunction can be seen in the figure.

[0125] (4) XRD pattern of FeSe / MnSe / NBC Figure 4 As shown, from Figure 4 It can be seen that the FeSe / MnSe / NBC crystal structure corresponds to that of FeSe (PDF#26-0795) and MnSe (PDF#11-0683). Therefore, the XRD results further confirm the formation of the FeSe / MnSe heterojunction.

[0126] The above test results (SEM, elemental analysis, TEM, XRD, etc.) of the sulfur storage materials prepared in Examples 2-4 are basically the same as those of the sulfur storage material prepared in Example 1, and will not be described in detail here.

[0127] 2. EPR response test was performed on FeSe / MnSe / NBC in Example 1, FeSe / C in Comparative Example 1 and MnSe / C in Comparative Example 2. The results are as follows: Figure 5 As shown, from Figure 5 It can be seen that the EPR response value of FeSe / MnSe / NBC is significantly stronger than that of MnSe / C and FeSe / C, indicating the existence of Se vacancies in FeSe / MnSe / NBC.

[0128] 3. The electrochemical performance of the lithium-sulfur battery positive electrode material (S / FeSe / MnSe / NBC) prepared in Example 5 and the lithium-sulfur battery positive electrode material (S / FeSe / C) prepared in Comparative Example 3 were tested.

[0129] (1) A lithium-sulfur battery positive electrode material (denoted as S / FeSe / MnSe / NBC) was used as the positive electrode material and a lithium sheet was used as the negative electrode material. A 2032 button-type lithium-sulfur battery was prepared according to an existing conventional method (the preparation of the 2032 button-type battery belongs to the existing technology and will not be repeated here). It is denoted as S / FeSe / MnSe / NBC lithium-sulfur battery.

[0130] (2) Using the lithium-sulfur battery positive electrode material (S / FeSe / C) as the positive electrode material and the lithium sheet as the negative electrode material, a 2032 button-type lithium-sulfur battery was prepared according to the existing conventional method, which was recorded as S / FeSe / C lithium-sulfur battery.

[0131] (3) The prepared S / FeSe / MnSe / NBC and S / FeSe / C lithium-sulfur batteries were subjected to charge and discharge tests (voltage range: 1.7-2.8 V, charging current 0.2 C, discharging current 0.2 C) and cycle tests (voltage range: 1.7-2.8 V, charging current 1.0 C, discharging current 1.0 C) in the Newwell test system.

[0132] The charge and discharge test results of S / FeSe / MnSe / NBC lithium-sulfur battery are as follows Figure 6 As shown, Figure 6 The sulfur loading on the surface is 1.5 mg cm -2 Under the condition of discharge rate of 0.2C, the discharge capacity of S / FeSe / MnSe / NBC lithium-sulfur battery is 1334mAh﹒g -1 .

[0133] The cycling test results of S / FeSe / MnSe / NBC lithium-sulfur battery are as follows Figure 7 As shown, Figure 7 The sulfur loading on the surface is 1.5 mg cm -2 Under the condition of discharge rate of 1.0C, the initial discharge specific capacity of S / FeSe / MnSe / NBC lithium-sulfur battery can reach 1018mAh﹒g -1 After 1000 stable cycles, the specific capacity is 727mAh﹒g -1 , the capacity decay per cycle is 0.029%.

[0134] The charge and discharge test results of S / FeSe / C lithium-sulfur battery are as follows Figure 8 As shown, Figure 8 The sulfur surface loading was 1.5 mg cm -2 Under the condition of discharge rate of 0.2C, the discharge capacity of S / FeSe / C lithium-sulfur battery is 897mAh﹒g -1Compared with the S / FeSe / MnSe / NBC lithium-sulfur battery in Example 5, the charge-discharge specific capacity of the S / FeSe / MnSe / NBC lithium-sulfur battery is higher.

[0135] The cycling test results of S / FeSe / C lithium-sulfur battery are shown in Figure 2. Figure 9 As shown, Figure 9 The sulfur loading on the surface is 1.5 mg cm -2 Under the condition of discharge rate of 1.0C, the initial discharge capacity of S / FeSe / C lithium-sulfur battery is 661mAh﹒g -1 After 1000 cycles, the specific capacity rapidly decayed to 70 mAh g -1 The capacity decay per cycle was 0.089%. Compared with the S / FeSe / MnSe / NBC lithium-sulfur battery in Example 5, the S / FeSe / MnSe / NBC lithium-sulfur battery has better cycle stability.

[0136] In addition, during the discharge process, the schematic diagram of the deposition process of polysulfide on the surface of S / FeSe / MnSe / NBC in Example 5 and S / FeSe / C in Comparative Example 3 is as follows: Figure 10 As shown. During the discharge process, lithium ions migrated from the negative electrode react with S in the positive electrode material S / FeSe / MnSe / NBC to generate polysulfides, and the FeSe / MnSe heterojunction boundary in the S / FeSe / MnSe / NBC preferentially and selectively adsorbs polysulfides, thereby causing the Li2S deposition layer to preferentially nucleate and grow in a 3D pattern at the boundary in a direction perpendicular to the boundary, thereby providing sufficient active sites and channels for the subsequent redox reaction of polysulfides (no Li2S is deposited on the surface of S / FeSe / MnSe / NBC); while in Comparative Example 3, the surface of S / FeSe / C uniformly adsorbs polysulfides and then converts them into a uniform and dense Li2S inert deposition layer, thereby hindering the continuous reaction of polysulfides.

[0137] In summary, the present invention provides a sulfur storage material, a lithium-sulfur battery positive electrode material, a preparation method, and a lithium-sulfur battery. The sulfur storage material of the present invention comprises a hollow carbon sphere doped with a non-metal atom and an Fe-containing X vacancy (Se vacancy, S vacancy, or N vacancy) embedded in the surface of the hollow carbon sphere. a X b / Mn c X d Heterojunction nanoparticles. Among them, the doping of non-metallic atoms can provide more polar sites for chemical adsorption of polysulfides, thereby inhibiting the shuttle of polysulfides, effectively avoiding the increase of negative electrode polarization caused by the shuttle of polysulfides to the negative electrode side; Fe a X b / Mn c X dHeterojunctions and X vacancies (Se vacancies, S vacancies, or N vacancies) can regulate the electronic structure distribution inside the material, increase the electronic conductivity of the material, improve catalytic performance, reduce the energy barrier of polysulfide redox reactions, and improve the performance of lithium-sulfur batteries; the hollow sphere structure can accommodate more sulfur, withstand the change in sulfur volume during charge and discharge, and avoid damage to the electrode material structure due to sulfur volume changes. In addition, during the discharge process, polysulfides are preferentially adsorbed on Fe a X b / Mn c X d At the heterojunction boundary, a vertical Li2S deposition layer is formed in a 3D pattern, effectively preventing surface passivation and providing sufficient active sites and channels for subsequent, continuous Li2S nucleation and deposition. Lithium-sulfur batteries fabricated using the sulfur storage material provided by this invention exhibit advantages such as high positive electrode conductivity and minimal volume change, minimal negative electrode polarization and rapid redox reaction kinetics, excellent charge-discharge performance, and a long cycle life.

[0138] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A sulfur storage material, characterized in that: The sulfur storage material includes hollow carbon spheres doped with non-metal atoms and FeSe / MnSe heterojunction nanoparticles containing Se vacancies embedded in the surface of the hollow carbon spheres; The non-metal atom is selected from N and B.

2. A method for preparing the sulfur storage material according to claim 1, characterized in that: Including steps: Adding iron salt, manganese salt, trimesic acid, organic polymer, and ionic liquid containing non-metallic elements into a solvent to obtain a mixed solution; the organic polymer is selected from at least one of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and polypropylene glycol; reacting the mixed solution at a first preset temperature for a first preset time to obtain a first precursor; calcining the first precursor at a second preset temperature for a second preset time under a hydrogen atmosphere to obtain a second precursor; The sulfur storage material is obtained by selenizing the second precursor at a third preset temperature for a third preset time.

3. The preparation method according to claim 2, characterized in that The mass ratio of the iron salt, manganese salt, trimesic acid, organic polymer, and ionic liquid containing non-metallic elements is (0.6-1): (0.2-0.4): (0.2-1): (1-3): (0.4-0.6).

4. The preparation method according to claim 2, characterized in that The iron salt is selected from at least one of ferric chloride, ferric nitrate, and ferric sulfate; And / or, the manganese salt is at least one selected from manganese nitrate, manganese chloride, and manganese sulfate; And / or, the ionic liquid containing non-metallic elements is selected from at least one of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-octyl-3-methylimidazolium tetrafluoroborate; And / or, the solvent is selected from at least one of water, ethanol, ethylene glycol, and N,N-dimethylformamide.

5. The preparation method according to claim 2, characterized in that The first preset temperature is 80-160°C, and the first preset time is 8-15 hours; And / or, the second preset temperature is 500-1000° C., and the second preset time is 2-8 hours; And / or, the third preset temperature is 300-800° C., and the third preset time is 2-6 hours.

6. A method for preparing a positive electrode material for a lithium-sulfur battery, characterized in that: Including steps: The sublimated sulfur is mixed with the sulfur storage material according to claim 1 and heated under sealed conditions to obtain the lithium-sulfur battery positive electrode material.

7. A lithium-sulfur battery positive electrode material, characterized in that: The positive electrode material of the lithium-sulfur battery is prepared by the preparation method of the positive electrode material of the lithium-sulfur battery according to claim 6.

8. A lithium-sulfur battery comprising a positive electrode sheet, characterized in that: The material of the positive electrode sheet includes the lithium-sulfur battery positive electrode material according to claim 7.

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