A lithium-sulfur battery cathode material, its preparation method and application

Abstract

This invention provides a lithium-sulfur battery cathode material, its preparation method, and its application. The preparation method includes the following steps: (1) mixing and stirring a cobalt source, CTAB, and CNT aqueous dispersion, adding 2-MIM, and reacting to obtain a composite material; (2) mixing a sulfide and a solvent to obtain a sulfide solution, adding the composite material obtained in step (1), and reacting to obtain a composite material of cobalt sulfide-organic framework and carbon nanotubes; (3) mixing the composite material obtained in step (2), PAN, and a solvent for electrospinning, mixing the obtained product with selenium disulfide, sintering, and then mixing with an oxidant solution to obtain the lithium-sulfur battery cathode material. This invention forms a core-shell network structure with nano-sulfur and cobalt sulfide particles embedded in a porous carbon framework as the core, a network of carbon nanotubes as the intermediate layer, and an outer layer of PAN / SeS2 fibers through a multi-step reaction.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, and relates to a lithium-sulfur battery cathode material, its preparation method, and its application. Background Technology

[0002] With industrial development, people have increasingly higher requirements for energy storage devices. Since traditional lithium-ion batteries have limited specific capacity and energy density, developing new energy batteries with higher capacity and energy density is of great significance. Lithium-sulfur batteries, with their specific capacity of 1675 mAh / g and energy density of 2600 Wh / kg, and the fact that elemental sulfur causes almost no pollution to the natural environment, have attracted widespread exploration and development from researchers.

[0003] Despite the numerous advantages of lithium-sulfur batteries, their development is severely hampered by several problems. First, the sulfur and lithium sulfide products of charging and discharging have poor conductivity, limiting the battery's rate performance. Second, the sulfur cathode undergoes significant volume changes before and after charging and discharging, easily damaging the electrode structure. Furthermore, during charging and discharging, the active material sulfur transforms into lithium polysulfides. Because these polysulfides are soluble in the electrolyte, they easily detach from the cathode, causing a shuttle effect to the anode, where they form lithium sulfide on the anode surface. This results in the loss of active material and the formation of lithium dendrites on the anode, which can puncture the separator and damage the battery. Therefore, developing a cathode that can suppress these problems and improve the performance of lithium-sulfur batteries is of great significance.

[0004] CN107768638A discloses a lithium-sulfur battery cathode material and a lithium-sulfur battery using the cathode material. It adopts an in-situ doping method to introduce iron and nitrogen together, and at the same time uses a hard template method to prepare a porous carbon material with iron and nitrogen heteroatoms.

[0005] CN110931737A discloses a lithium-sulfur battery cathode material, which incorporates GDC (Ce) into the lithium-sulfur battery cathode material. 1-x Gd x O 2-δ In addition to nickel, GDC can suppress the shuttle effect of polysulfides and improve the redox catalytic performance of lithium-sulfur battery cathode materials. Ni and GDC can combine to have high electronic conductivity and ion vacancies, thereby improving the conductivity of lithium-sulfur battery cathode materials.

[0006] Although the addition of conductive materials, catalytic particles, and porous structures has significantly improved the overall performance of batteries, the limited improvement is due to the lack of integration of these technologies, while the slightly higher cost is due to their combination. In addition, most current methods involve preparing sulfur-loaded materials for use in the cathode. As an externally added substance, sulfur inevitably remains on the surface of the material. During the charging and discharging process, this sulfur forms polysulfides and detaches from the cathode, resulting in a decrease in battery performance. Summary of the Invention

[0007] The purpose of this invention is to provide a lithium-sulfur battery cathode material, its preparation method, and its application. This invention forms a core-shell network structure with nano-sulfur and cobalt sulfide particles embedded in a porous carbon skeleton as the core, a network of carbon nanotubes as the middle layer, and PAN / SeS2 fibers as the outer layer through a multi-step reaction.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a lithium-sulfur battery cathode material, the method comprising the following steps:

[0010] (1) Cobalt source, hexadecyltrimethylammonium bromide (CTAB) and carbon nanotube aqueous dispersion were mixed and stirred, and 2-methylimidazolium (2-MIM) was added to react and obtain carbon nanotube-metal-organic framework composite material;

[0011] (2) Mix the sulfide and the solvent to obtain a sulfide solution, add the carbon nanotube-metal-organic framework composite material obtained in step (1), and react to obtain a composite material of cobalt sulfide-organic framework and carbon nanotube.

[0012] (3) The cobalt sulfide-organic framework and carbon nanotube composite material obtained in step (2), polyacrylonitrile (PAN) and solvent are mixed and electrospun. The resulting product is mixed with selenium disulfide, sintered and then mixed with an oxidant solution to obtain the lithium-sulfur battery cathode material.

[0013] In the preparation method described in this invention, the presence of a cobalt source serves as a formation site for the metal-organic framework (MOF) material. After mixing with a CNT solution, Co ions are uniformly distributed within the network of CNTs, allowing the subsequently formed ZIF-67 (Co-based MOF material) nanoparticles to be uniformly distributed within the network, forming nodes and enhancing the structural stability of the composite material. Simultaneously, the addition of CTAB causes the organic framework surrounding the Co particles to grow in a directional manner, transforming the ZIF-67, which would normally grow as dodecahedrons, into a hexahedron shape. This enhances the mechanical properties of the ZIF-67 particles, making them less prone to breakage and strengthening the network stability. Furthermore, the excellent electrical conductivity of CNTs gives the material excellent electron transport capabilities; while the unique porous structure of MOF materials and the large number of CNT network pathways result in excellent lithium-ion transport capabilities.

[0014] Preferably, the cobalt source in step (1) includes cobalt nitrate.

[0015] Preferably, the mass ratio of the cobalt source to the cetyltrimethylammonium bromide is (48-96):(1-2), for example: 48:1, 60:2, 80:1.5, 90:1.6 or 96:1, etc.

[0016] Preferably, the mass concentration of the carbon nanotube aqueous dispersion is 8-15%, for example: 8%, 9%, 10%, 12% or 15%, etc.

[0017] Before preparing ZIF-67, the cobalt source described in this invention is uniformly mixed with CNT aqueous dispersion, so that the subsequently grown ZIF-67 is fixed on the CNT network to form nodes, thereby improving the material stability. When preparing ZIF-67, CTAB is added to change the material growth direction from a regular dodecahedron to a cube, which improves the mechanical properties of ZIF-67 particles and makes them less prone to breakage.

[0018] Preferably, the mass ratio of the cobalt source to the carbon nanotubes in the carbon nanotube aqueous dispersion is (1.2-2.4):(1-2), for example: 1.2:1, 1.5:1.3, 1.8:1, 2:1.6 or 2.4:1, etc.

[0019] Preferably, deionized water is added during the mixing and stirring process.

[0020] Preferably, the mass ratio of 2-methylimidazole to cobalt source in step (1) is (11-22):(1.2-2.4), for example: 11:2.4, 15:2, 18:1.4, 20:1.5 or 22:1.2, etc.

[0021] Preferably, stirring is performed during the reaction.

[0022] Preferably, the reaction time is 4 to 6 hours, for example: 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours.

[0023] Preferably, the material obtained from the reaction is centrifuged.

[0024] Preferably, the centrifugation speed is 6000-8000 rpm, for example: 6000 rpm, 6500 rpm, 7000 rpm, 7500 rpm or 8000 rpm.

[0025] Preferably, the centrifugation time is 10 to 20 minutes, for example: 10 minutes, 12 minutes, 15 minutes, 18 minutes or 20 minutes.

[0026] Preferably, the centrifugation process is followed by drying.

[0027] Preferably, the drying temperature is 60-80°C, for example: 60°C, 65°C, 70°C, 75°C or 80°C.

[0028] Preferably, the drying time is 12 to 24 hours, for example: 12 hours, 15 hours, 18 hours, 20 hours or 24 hours.

[0029] Preferably, the sulfide in step (2) includes sodium sulfide.

[0030] The ZIF-67 of this invention reacts with sodium sulfide in a water bath to form CoS at the position of Co nanoparticles. In addition to providing the active substance sulfur, it can also inhibit the desorption of lithium polysulfides.

[0031] Preferably, the solvent includes deionized water.

[0032] Preferably, the mass concentration of the sulfide solution is 2-8%, for example: 2%, 3%, 4%, 5% or 8%, etc.

[0033] Preferably, the mass ratio of the carbon nanotube-metal-organic framework composite material to the sulfide is (5-10):(2-4), for example: 5:4, 6:3, 8:2, 9:3 or 10:2, etc.

[0034] Preferably, the reaction temperature in step (2) is 150 to 200°C, for example: 150°C, 160°C, 170°C, 180°C, 190°C or 200°C.

[0035] Preferably, the reaction time is 12 to 16 hours, for example: 12 hours, 13 hours, 14 hours, 15 hours or 16 hours.

[0036] Preferably, the material obtained from the reaction is centrifuged.

[0037] Preferably, the centrifugation speed is 6000-8000 rpm, for example: 6000 rpm, 6500 rpm, 7000 rpm, 7500 rpm or 8000 rpm.

[0038] Preferably, the centrifugation time is 10 to 20 minutes, for example: 10 minutes, 12 minutes, 15 minutes, 18 minutes or 20 minutes.

[0039] Preferably, the centrifugation process is followed by drying.

[0040] Preferably, the drying temperature is 60-80°C, for example: 60°C, 65°C, 70°C, 75°C or 80°C.

[0041] Preferably, the drying time is 8 to 12 hours, for example: 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0042] Preferably, the mass ratio of the cobalt sulfide-organic framework-carbon nanotube composite material and polyacrylonitrile in step (3) is (2-4):(5-10), for example: 2:10, 2.5:8, 3:6, 3.5:6 ​​or 4:5, etc.

[0043] Preferably, the solvent includes dimethylformamide.

[0044] Preferably, stirring is performed during the mixing process.

[0045] Preferably, the stirring time is 6 to 8 hours, for example: 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours.

[0046] Preferably, the voltage of the electrospinning treatment is 10-15kV, for example: 10kV, 11kV, 12kV, 13kV, 14kV or 15kV, etc.

[0047] Preferably, the current for the electrospinning process is 1 to 2 mA, for example: 1 mA, 1.2 mA, 1.5 mA, 1.8 mA or 2 mA, etc.

[0048] Preferably, the dripping rate of the electrospinning treatment is 0.2 to 0.4 mL / min, for example: 0.2 mL / min, 0.25 mL / min, 0.3 mL / min, 0.35 mL / min or 0.4 mL / min, etc.

[0049] The electrospinning technology described in this invention prepares core-shell structured composite material @PAN fibers, which can effectively allow lithium ions to pass through while inhibiting the release of lithium polysulfides.

[0050] Preferably, the mass ratio of the product obtained from the electrospinning treatment to selenium disulfide is (4-6):(10-20), for example: 4:20, 4.5:18, 5:15, 5.5:12 or 6:10, etc.

[0051] The composite of CoS-MOF@CNT@PAN fibers obtained through electrospinning and SeS2 improves the material's structural density, stability, and sulfur loading capacity. This allows for the formation of a more structurally stable SEI film on the positive electrode surface during discharge, thereby enhancing the overall battery capacity and stability.

[0052] Preferably, the sintering temperature in step (3) is 450 to 550°C, for example: 450°C, 480°C, 500°C, 520°C or 550°C.

[0053] Preferably, the sintering treatment time is 6 to 8 hours, for example: 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours.

[0054] Preferably, the oxidant solution comprises a ferric chloride solution.

[0055] Fe in the oxidant solution of the present invention 3+ Converting some CoS to S improves the electrochemical kinetics of the reaction between the material and lithium ions, thus enhancing the battery's rate performance; retaining some Co particles can maintain the stable network structure of the material's core.

[0056] Preferably, the molar concentration of the ferric chloride solution is 1 to 2 mol / L, for example: 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L, etc.

[0057] Preferably, the settling time after mixing is 8 to 12 hours, for example: 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0058] Preferably, the centrifugation process is performed after the settling period.

[0059] Preferably, the centrifugation speed is 6000-8000 rpm, for example: 6000 rpm, 6500 rpm, 7000 rpm, 7500 rpm or 8000 rpm.

[0060] Preferably, the centrifugation time is 10 to 20 minutes, for example: 10 minutes, 12 minutes, 15 minutes, 18 minutes or 20 minutes.

[0061] In a second aspect, the present invention provides a lithium-sulfur battery cathode material, which is prepared by the method described in the first aspect, and the lithium-sulfur battery cathode material includes a core and an intermediate layer and an outer layer sequentially stacked on the surface of the core.

[0062] The numerous micropores, channels, and nanoparticles in the material described in this invention can simultaneously mitigate volume changes, effectively adsorb lithium polysulfides, and significantly suppress the shuttle effect. Furthermore, the carbon network and porous carbon significantly improve the material's conductivity and lithium-ion transport capacity, thereby substantially enhancing the rate performance and cycle life of lithium-sulfur batteries. Additionally, the carbon framework material is located at the nodes of the carbon network, improving the material's structural stability. Moreover, the material itself contains the active substance sulfur, eliminating the need for external addition and further preventing the shuttle effect.

[0063] Preferably, the core comprises a porous carbon framework and nano-sulfur and cobalt sulfide particles embedded in the porous carbon framework.

[0064] Preferably, the intermediate layer comprises a network of carbon nanotubes.

[0065] In the lithium-sulfur battery cathode material of this invention, the presence of sulfur particles in the S / CoS-porous carbon@CNT, which serves as the core and intermediate layer, allows the material to react with more lithium ions. Furthermore, since the sulfur particles were previously combined with Co particles, they are almost entirely located at the nodes of the CNT network, making them difficult to detach and significantly suppressing the shuttle effect of polysulfides. However, Co exists in the network as nanoparticles, resulting in an excessively dense distribution of Co in the mesh material. Reducing most of the Co particles can significantly improve the electrochemical kinetics of the overall material's reaction with lithium ions; while retaining some Co particles has little impact on the material's electrochemical performance and allows them to be evenly distributed at the nodes of the carbon network, maintaining network stability. Additionally, the organic framework of the MOF material transforms into an inorganic porous carbon structure after sintering, with a significantly increased pore size, effectively mitigating volume changes during the charge-discharge process of the lithium-sulfur battery and increasing electrode lifespan.

[0066] Preferably, the outer layer comprises a PAN / SeS2 composite material with a core-shell network structure.

[0067] In the lithium-sulfur battery cathode material of this invention, the PAN fiber composite SeS2 serving as the outer shell makes the material structure more compact and stable, allowing the SEI film formed during discharge to form on the fiber surface, thus making the system more stable and reducing capacity decay during cycling. Furthermore, the porous framework itself provides numerous lithium-ion transport channels, reducing transport obstacles. In addition, the presence of SeS2 provides a large number of active sulfur particles, which can attract more lithium-ions, thereby increasing the energy density of the lithium-sulfur battery. The chemical relationship with sulfur allows Se particles to chemically adsorb polysulfides, suppressing the shuttle effect and improving electrochemical performance.

[0068] Thirdly, the present invention provides a lithium-sulfur battery cathode, wherein the lithium-sulfur battery cathode comprises the lithium-sulfur battery cathode material as described in the second aspect.

[0069] Fourthly, the present invention provides a lithium-sulfur battery comprising a lithium-sulfur battery positive electrode as described in the third aspect.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] (1) This invention develops a high-porosity, high-sulfur material as a cathode. The numerous micropores, channels, and nanoparticles in the material simultaneously mitigate volume changes, effectively adsorb lithium polysulfides, and significantly suppress the shuttle effect. Furthermore, the carbon network and porous carbon significantly improve the material's conductivity and lithium-ion transport capacity, thereby greatly enhancing the rate performance and cycle performance of lithium-sulfur batteries. Additionally, the carbon framework material is located at the nodes of the carbon network, improving the material's structural stability. Moreover, the material itself contains the active substance sulfur, eliminating the need for external addition and further avoiding the shuttle effect.

[0072] (2) Using the present invention as the positive electrode material for lithium-sulfur batteries to assemble coin cells can achieve excellent electrochemical performance. Under a charge-discharge rate of 0.33C, the positive electrode active material has a first-cycle specific capacity of up to 1518 mAh / g and can maintain 1193 mAh / g after 100 cycles, which is significantly higher than other schemes used as comparison samples. Attached Figure Description

[0073] Figure 1 This is a comparison chart of the capacity cycling curves of the cathode materials prepared in Examples 1, 2 and 3.

[0074] Figure 2 This is a comparison chart of the capacity cycling curves of the cathode materials prepared in Example 1 and Comparative Examples 1-5. Detailed Implementation

[0075] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0076] Example 1

[0077] This embodiment provides a lithium-sulfur battery cathode material, and the preparation method of the lithium-sulfur battery cathode material is as follows:

[0078] (1) Dissolve 1.2 g of cobalt nitrate hexahydrate, 25 mg of CTAB and 10 ml of 10% multi-walled carbon nanotube aqueous dispersion in 50 ml of deionized water and stir at room temperature for 2 h. Then add 11 g of 2-MIM, continue stirring for 4 h and centrifuge to dry to obtain ZIF-67@CNT powder;

[0079] (2) Weigh 2g of sodium sulfide solid, dissolve it in 50ml of deionized water and place it in a hydrothermal reactor. Then add 5g of ZIF-67@CNT powder, heat at 200℃ for 12h, then centrifuge, wash and dry to obtain CoS-MOF@CNT composite material.

[0080] (3) 2g of CoS-MOF@CNT composite material and 5g of PAN powder were added to 10ml of DMF solvent and stirred at room temperature for 6h. Then, the solution was electrospun at 15kV and 2mA to obtain fibers. Then, 4g of fibers and 10g of SeS2 were heated in an argon atmosphere at 500℃ for 6h. After cooling, the material was immersed in a 1mol / L FeCl3 solution, sealed and allowed to stand for 12h. Finally, the precipitate was centrifuged, washed and dried to obtain the lithium-sulfur battery cathode material.

[0081] Example 2

[0082] This embodiment provides a lithium-sulfur battery cathode material, and the preparation method of the lithium-sulfur battery cathode material is as follows:

[0083] (1) Dissolve 2g of cobalt nitrate hexahydrate, 35mg of CTAB and 10ml of 10% multi-walled carbon nanotube aqueous dispersion in 50ml of deionized water and stir at room temperature for 2h. Then add 15g of 2-MIM, continue stirring for 4h and centrifuge to dry to obtain ZIF-67@CNT powder;

[0084] (2) Weigh 3g of sodium sulfide solid, dissolve it in 50ml of deionized water and place it in a hydrothermal reactor. Then add 8g of ZIF-67@CNT powder, heat at 180℃ for 12h, then centrifuge, wash and dry to obtain CoS-MOF@CNT composite material.

[0085] (3) 3g of CoS-MOF@CNT composite material and 8g of PAN powder were added to 15ml of DMF solvent and stirred at room temperature for 6h. Then the solution was electrospun at 12kV and 1.8mA to obtain fibers. Then 5g of fibers and 15g of SeS2 were heated in an argon atmosphere at 500℃ for 6h. After cooling, the material was immersed in a 1mol / L FeCl3 solution, sealed and allowed to stand for 12h. Finally, the precipitate was centrifuged, washed and dried to obtain the lithium-sulfur battery cathode material.

[0086] Example 3

[0087] The only difference between this embodiment and Embodiment 1 is that the mass ratio of the cobalt source to carbon nanotubes is 1:3, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0088] Comparative Example 1

[0089] This comparative example uses conventional graphite and sublimed sulfur to prepare lithium-sulfur battery cathode materials.

[0090] Comparative Example 2

[0091] The only difference between this comparative example and Example 1 is that CTAB is not added; all other conditions and parameters are exactly the same as in Example 1.

[0092] Comparative Example 3

[0093] The only difference between this comparative example and Example 1 is that carbon nanotubes are not added; all other conditions and parameters are exactly the same as in Example 1.

[0094] Comparative Example 4

[0095] The only difference between this comparative example and Example 1 is that electrospinning is not performed; all other conditions and parameters are exactly the same as in Example 1.

[0096] Comparative Example 5

[0097] The only difference between this comparative example and Example 1 is that ferric chloride solution is not used for treatment; all other conditions and parameters are exactly the same as in Example 1.

[0098] Battery fabrication and performance testing:

[0099] Powders prepared using different methods were mixed and ground with Ketjen Black and polyvinylidene fluoride (PVDF) powders at a mass ratio of 8:1:1 for 30 minutes, baked, and then N-methylpyrrolidone (NMP) was added to prepare the positive electrode slurry. The slurry was poured onto a 12μm aluminum foil, and a coating thickness of 188μm was controlled using a coating machine. After coating, the electrode sheet was baked, pressed, cut, and assembled into coin cells.

[0100] Inductively coupled plasma optical emission spectrometry (ICP) was used to determine the sulfur (S) content in the powders prepared by different methods. The S content of the active material in the battery was determined based on the amount of coating on the positive electrode, the proportion of the main positive electrode material, and the S content in the main material. The 0.33C current of the batteries prepared by each method was calibrated based on the theoretical specific capacity of S, and a charge-discharge cycle of "20 min rest – 0.33C charging to 2.8V – 20 min rest – 0.33C discharging to 1.7V" was established, and this cycle was repeated 100 times.

[0101] The test results are shown in Table 1:

[0102] Table 1

[0103]

[0104]

[0105] As shown in Table 1, based on Examples 1-2, the specific capacity of the battery's positive electrode in the first cycle can reach over 1486 mAh / g, and after 5 cycles of 0.33C charge-discharge, over 81% of the specific capacity can be retained. From the 5th to the 100th cycle, the average capacity decay is 0.03% / cycle, reaching a relatively high level in the field.

[0106] A comparison of Examples 1 and 3 shows that, during the preparation of the lithium-sulfur battery cathode material of the present invention, the mass ratio of the cobalt source to the carbon nanotubes in the carbon nanotube aqueous dispersion affects the performance of the cathode material. Controlling the mass ratio of the cobalt source to the carbon nanotubes in the carbon nanotube aqueous dispersion at (1.2–2.4):(1–2) yields a cathode material with better performance. If the amount of carbon nanotubes added is too high, the proportion of sulfur loaded as an active substance in the material will decrease slightly, and too many CNTs will cause some of them to be unable to be fixed by the carbon framework material, thereby reducing the stability of the material structure.

[0107] The capacity cycling curves of the cathode materials prepared in Example 1 and Comparative Example 1 are compared as follows: Figure 1 As shown, a comparison between Example 1 and Comparative Example 1 reveals that, compared to traditional lithium-sulfur battery cathode materials, the numerous micropores, channels, and nanoparticles in the material of this invention can simultaneously mitigate volume changes, effectively adsorb lithium polysulfides, and significantly suppress the shuttle effect. Furthermore, the carbon network and porous carbon significantly improve the material's conductivity and lithium-ion transport capacity, thereby substantially enhancing the rate performance and cycle performance of lithium-sulfur batteries. Additionally, the carbon framework material is located at the nodes of the carbon network, improving the material's structural stability. Moreover, the material itself contains the active substance sulfur, eliminating the need for external addition and further preventing the shuttle effect.

[0108] As can be seen from the comparison between Example 1 and Comparative Example 2, the addition of CTAB causes the organic framework outside the Co particles to grow in a more directional manner, making ZIF-67, which should have grown as a dodecahedron, into a hexahedron shape. This enhances the mechanical properties of the ZIF-67 particles, making them less prone to breakage and strengthening the stability of the network.

[0109] As can be seen from the comparison between Example 1 and Comparative Example 3, CNTs have good conductivity, which gives the material excellent electron transport capability; while the unique porous structure of MOF materials and the large number of CNT network pathways make the material's lithium-ion transport capability very good as well.

[0110] As can be seen from the comparison between Example 1 and Comparative Example 4, the PAN fiber composite SeS2 used as the shell makes the material structure more compact and stable, which allows the SEI film formed by discharge to form on the fiber surface, making the system more stable and reducing capacity decay during cycling; and the porous framework itself provides a large number of lithium-ion transport channels, reducing transport obstacles.

[0111] A comparison of Example 1 and Comparative Example 5 shows that using Fe... 3+ Converting some CoS to S improves the electrochemical kinetics of the reaction between the material and lithium ions, thus enhancing the battery's rate performance; retaining some Co particles can maintain the stable network structure of the material's core.

[0112] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a lithium-sulfur battery cathode material, characterized in that, The preparation method includes the following steps: (1) Cobalt source, hexadecyltrimethylammonium bromide and carbon nanotube aqueous dispersion are mixed and stirred, 2-methylimidazole is added, and carbon nanotube-metal-organic framework composite material is obtained by reaction; the mass ratio of cobalt source and carbon nanotube in carbon nanotube aqueous dispersion is (1.2~2.4):(1~2); (2) The sulfide and solvent are mixed to obtain a sulfide solution, and the carbon nanotube-metal-organic framework composite material obtained in step (1) is added to react and obtain a composite material of cobalt sulfide-organic framework and carbon nanotube. (3) The cobalt sulfide-organic framework and carbon nanotube composite material obtained in step (2), polyacrylonitrile and solvent are mixed and electrospun. The resulting product is mixed with selenium disulfide, sintered and then mixed with oxidant solution and left to stand for 8-12 hours. After centrifugation, the lithium-sulfur battery cathode material is obtained. The sintering process in step (3) is carried out at a temperature of 450~550℃ for 6~8 hours. The oxidant solution in step (3) includes a ferric chloride solution; Step (3) yields the lithium-sulfur battery cathode material comprising a core and an intermediate layer and an outer layer sequentially stacked on the surface of the core.

2. The preparation method according to claim 1, characterized in that, The cobalt source in step (1) includes cobalt nitrate.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the cobalt source to the hexadecyltrimethylammonium bromide is (48~96):(1~2).

4. The preparation method according to claim 1, characterized in that, The mass concentration of the carbon nanotube aqueous dispersion is 8-15%.

5. The preparation method according to claim 1, characterized in that, Deionized water is added during the mixing process.

6. The preparation method according to claim 1, characterized in that, The mass ratio of 2-methylimidazole to cobalt source in step (1) is (11~22):(1.2~2.4).

7. The preparation method according to claim 1, characterized in that, Stirring is performed during the reaction described in step (1).

8. The preparation method according to claim 1, characterized in that, The reaction time in step (1) is 4 to 6 hours.

9. The preparation method according to claim 1, characterized in that, Step (1) The material obtained from the reaction is centrifuged.

10. The preparation method according to claim 9, characterized in that, The centrifugation speed is 6000~8000 rpm.

11. The preparation method according to claim 9, characterized in that, The centrifugation time is 10-20 minutes.

12. The preparation method according to claim 9, characterized in that, The centrifugation process is followed by drying.

13. The preparation method according to claim 12, characterized in that, The drying process is carried out at a temperature of 60~80℃.

14. The preparation method according to claim 12, characterized in that, The drying process takes 12 to 24 hours.

15. The preparation method according to claim 1, characterized in that, The sulfide in step (2) includes sodium sulfide.

16. The preparation method according to claim 1, characterized in that, The solvent in step (2) includes deionized water.

17. The preparation method according to claim 1, characterized in that, The mass concentration of the sulfide solution in step (2) is 2-8%.

18. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the carbon nanotube-metal-organic framework composite material to the sulfide is (5~10):(2~4).

19. The preparation method according to claim 1, characterized in that, The reaction temperature in step (2) is 150~200℃.

20. The preparation method according to claim 1, characterized in that, The reaction time in step (2) is 12-16 hours.

21. The preparation method according to claim 1, characterized in that, Step (2) The material obtained from the reaction is centrifuged.

22. The preparation method according to claim 21, characterized in that, The centrifugation speed is 6000~8000 rpm.

23. The preparation method according to claim 21, characterized in that, The centrifugation time is 10-20 minutes.

24. The preparation method according to claim 21, characterized in that, The centrifugation process is followed by drying.

25. The preparation method according to claim 24, characterized in that, The drying process is carried out at a temperature of 60~80℃.

26. The preparation method according to claim 24, characterized in that, The drying process takes 8 to 12 hours.

27. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the cobalt sulfide-organic framework-carbon nanotube composite material to polyacrylonitrile is (2~4):(5~10).

28. The preparation method according to claim 1, characterized in that, The solvent in step (3) includes dimethylformamide.

29. The preparation method according to claim 1, characterized in that, Step (3) involves stirring during the mixing of the cobalt sulfide-organic framework-carbon nanotube composite material, polyacrylonitrile, and solvent.

30. The preparation method according to claim 29, characterized in that, The stirring time in step (3) is 6-8 hours.

31. The preparation method according to claim 1, characterized in that, The voltage for the electrospinning process in step (3) is 10~15kV.

32. The preparation method according to claim 1, characterized in that, The current for the electrospinning process in step (3) is 1~2mA.

33. The preparation method according to claim 1, characterized in that, The dripping rate of the electrospinning process in step (3) is 0.2~0.4 mL / min.

34. The preparation method according to claim 1, characterized in that, The mass ratio of the product obtained by electrospinning in step (3) to selenium disulfide is (4~6):(10~20).

35. The preparation method according to claim 1, characterized in that, The molar concentration of the ferric chloride solution in step (3) is 1~2 mol / L.

36. The preparation method according to claim 1, characterized in that, The centrifugation speed is 6000~8000 rpm.

37. The preparation method according to claim 1, characterized in that, The centrifugation time is 10-20 minutes.

38. A lithium-sulfur battery cathode material, characterized in that, The lithium-sulfur battery cathode material is prepared by the method described in any one of claims 1-36, and the lithium-sulfur battery cathode material includes a core and an intermediate layer and an outer layer sequentially stacked on the surface of the core.

39. The lithium-sulfur battery cathode material according to claim 38, characterized in that, The core comprises a porous carbon framework and nano-sulfur and cobalt sulfide particles embedded in the porous carbon framework.

40. The lithium-sulfur battery cathode material according to claim 38, characterized in that, The intermediate layer comprises a network of carbon nanotubes.

41. The lithium-sulfur battery cathode material according to claim 38, characterized in that, The outer layer comprises a PAN / SeS2 composite material with a core-shell network structure.

42. A lithium-sulfur battery cathode, characterized in that, The lithium-sulfur battery cathode comprises the lithium-sulfur battery cathode material as described in any one of claims 38-41.

43. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery includes the lithium-sulfur battery positive electrode as described in claim 42.

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