Preparation method of positive electrode material, positive electrode material, and lithium-sulfur battery

Abstract

A method for preparing a positive electrode material, a positive electrode material, and a lithium-sulfur battery. The method comprises pretreating carbon nanotubes to obtain open carbon nanotubes; placing the open carbon nanotubes in a container and evacuating the container to a vacuum degree of 0.05 Pa to 0.1 Pa; maintaining the vacuum degree, injecting a metal catalyst solution into the container to impregnate the open carbon nanotubes to obtain a precursor mixture; drying and heat-treating the precursor mixture to convert the metal catalyst into metal particles that fill the interior of the open carbon nanotubes to obtain a carbon nanotube composite material; and adding sulfur to the carbon nanotube composite material, grinding it, and heating it to obtain the positive electrode material. The present application utilizes a negative pressure liquid phase method to efficiently coat the metal catalyst within the carbon nanotubes, thereby improving the catalytic activity and stability of the catalyst, reducing the shuttle effect in the lithium-sulfur battery, and improving the longevity and stability of the positive electrode material.

Description

Technical Field

[0001] The present application relates to the technical field of positive electrode materials, and in particular to a method for preparing a positive electrode material, a positive electrode material, and a lithium-sulfur battery. Background Art

[0002] With the increasing global demand for renewable energy and electric vehicles, traditional lithium-ion batteries face the dual challenges of energy density and cost. Lithium-sulfur batteries have become a hot topic of research due to their high theoretical capacity, high energy density, and low cost. Lithium-sulfur batteries use sulfur as the positive electrode material. Compared to the cobalt and nickel used in traditional lithium-ion batteries, sulfur is abundant and low-cost, helping to reduce dependence on rare metals and environmental impact.

[0003] However, based on the inherent reaction mechanism of lithium-sulfur batteries, lithium-sulfur batteries currently have the following problems: First, due to the S8 (5×10 -30 S cm -1 ) and Li2S (3.6×10 -7 S cm -1 )'s insulation, resulting in low active material utilization during the charge and discharge process. Secondly, the lithium polysulfides produced during the charge and discharge process dissolve in the electrolyte, causing a "shuttle effect" between the positive and negative electrodes, leading to significant loss of active material, rapid capacity decay, and corrosion of the lithium negative electrode. Introducing catalysts is an effective strategy to address these issues, but current catalysts used in lithium-sulfur batteries suffer from issues such as excessive catalyst dosage, poisoning by the reaction between the catalyst and polysulfides, and excessive adsorption of polysulfides. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, an embodiment of the present application provides a method for preparing a positive electrode material.

[0005] In addition, the embodiments of the present application also provide a positive electrode material prepared by the aforementioned preparation method and a lithium-sulfur battery using the positive electrode material.

[0006] The present invention provides a method for preparing a positive electrode material, which comprises the following steps:

[0007] pre-treating the carbon nanotubes to obtain open carbon nanotubes;

[0008] Placing the open carbon nanotubes in a container, and evacuating the container to a vacuum degree of 0.05 Pa to 0.1 Pa;

[0009] maintaining the vacuum degree, injecting a metal catalyst solution into the container to impregnate the open carbon nanotubes to obtain a precursor mixture;

[0010] drying and heat-treating the precursor mixture to convert the metal catalyst into metal particles that fill the interior of the open carbon nanotubes to obtain a carbon nanotube composite material; and

[0011] Sulfur is added to the carbon nanotube composite material, followed by grinding and heating to obtain the positive electrode material.

[0012] In some possible embodiments, the carbon nanotubes are aligned carbon nanotubes, and the aligned carbon nanotubes include at least one of carbon nanotube arrays, aligned multi-walled carbon nanotubes, and aligned double-walled carbon nanotubes; and / or

[0013] The purity of the carbon nanotubes is lower than 99%.

[0014] In some possible embodiments, the metal catalyst solution includes at least one of CoCl2, Co(NO3)2, FeCl3, Fe(NO3)3, NiCl3, Ni(NO3)3, ZnCl2 and Zn(NO3)2; and / or

[0015] The concentration of the metal catalyst solution is 1 g / L to 5 g / L.

[0016] In some possible embodiments, in the precursor mixture, the mass ratio of the metal catalyst solution to the open carbon nanotubes is (0.1-0.5):1.

[0017] In some possible embodiments, the step of impregnating the open-ended carbon nanotubes with the metal catalyst solution further includes:

[0018] The metal catalyst solution and the open carbon nanotubes are stirred for 3 to 5 hours.

[0019] In some possible embodiments, when the container is evacuated, the temperature inside the container is 60° C. to 80° C.

[0020] In some possible embodiments, in the heat treatment step, the heat treatment temperature is 400° C. to 800° C., and the heat treatment time is 3 h to 5 h.

[0021] The present invention provides a positive electrode material prepared by the aforementioned positive electrode material preparation method. The positive electrode material includes a carbon nanotube composite material and sulfur supported on the carbon nanotube composite material, wherein the carbon nanotube composite material includes open carbon nanotubes and metal particles located within the open carbon nanotubes.

[0022] An embodiment of the present application also provides a lithium-sulfur battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet includes the aforementioned positive electrode material.

[0023] Compared with the existing technology, the preparation method of the positive electrode material provided in the embodiment of the present application can quickly introduce the metal catalyst solution into the interior of the carbon nanotubes by utilizing liquid phase negative pressure filling technology under a certain vacuum degree, and then convert the internal metal catalyst into metal particles through subsequent heat treatment, and finally obtain a positive electrode material in which the metal particles are coated inside the carbon nanotubes.

[0024] The cathode materials provided by the embodiments of the present application, because the metal catalyst is encapsulated within carbon nanotubes, reduce the risk of polysulfides generated during the cathode material's lithium-sulfur battery reaction coming into direct contact with the metal catalyst, leading to sulfidation and loss of catalytic activity. This improves the stability and catalytic activity of the metal catalyst, thereby reducing the amount of metal particle catalyst used. Furthermore, the barrier effect of the carbon nanotubes weakens the strong adsorption between the metal particle catalyst and polysulfides, freeing up the metal particle catalyst's active catalytic sites, thereby improving catalytic reaction efficiency and effectively adsorbing and rapidly catalytically converting polysulfides, thereby reducing the shuttle effect in lithium-sulfur batteries. Furthermore, the combination of the metal particle catalyst and carbon nanotubes creates an effective conductive framework, improving the conductivity of the cathode material and sulfur utilization, thereby increasing the capacity of the lithium-sulfur battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a process flow chart of the method for preparing the positive electrode material provided in the embodiment of the present application.

[0026] Figure 2 This is a charge and discharge performance diagram of a battery prepared using the positive electrode materials provided in Example 1 and Comparative Example 1 of the present application.

[0027] Figure 3 The cycling performance diagram of the battery prepared with the positive electrode materials provided in Example 1 and Comparative Example 1 of the present application.

[0028] Figure 4 This is a transmission electron microscope image of the positive electrode material provided in Example 1 of the present application.

[0029] Figure 5 This is a thermogravimetric curve of the positive electrode material provided in Example 1 of the present application in air. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making any creative work shall fall within the scope of protection of the present application.

[0031] See also Figure 1 As shown, the embodiment of the present application provides a method for preparing a positive electrode material, which comprises the following steps:

[0032] Step S1: pre-treating the carbon nanotubes to obtain open carbon nanotubes.

[0033] In step S1, the carbon nanotubes can be pretreated by shortening and opening the carbon nanotubes using a nitric acid solution, and the opened carbon nanotubes are collected and purified by filtration and drying. It is understood that any method that can pretreat the carbon nanotubes by shortening and opening the carbon nanotubes includes, but is not limited to, the aforementioned nitric acid solution treatment, other acidic solution treatment, oxidizing atmosphere treatment, or plasma treatment.

[0034] In some embodiments, the carbon nanotubes may be aligned carbon nanotubes. Compared to disordered carbon nanotubes, aligned carbon nanotubes are more conducive to the ingress of metal salt solutions after vacuuming and have better mechanical and electrical properties, thereby further improving the stability and electrochemical performance of the positive electrode material. The aligned carbon nanotubes may include at least one of carbon nanotube arrays, aligned multi-walled carbon nanotubes, and aligned double-walled carbon nanotubes.

[0035] In some embodiments, the concentration of the nitric acid solution can be 8 mol / L to 16 mol / L, which is beneficial for pre-treating the carbon nanotubes by shortening and opening them. The concentration of the nitric acid solution can further be 10 mol / L to 14 mol / L, and illustratively can be 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, 12 mol / L, 13 mol / L, 14 mol / L, 15 mol / L, or 16 mol / L.

[0036] In some embodiments, the ratio of carbon nanotubes to nitric acid solution can be 10 g / L to 50 g / L, which is beneficial for further improving the opening effect. The specific ratio can be further adjusted according to production requirements. The ratio of carbon nanotubes to nitric acid solution can further be 15 g / L to 25 g / L, and can be 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, or 50 g / L, for example.

[0037] In some embodiments, the heating temperature in step S1 can be 130° C. to 140° C., which is beneficial for further improving the pretreatment effect and efficiency and accelerating the reaction process between the carbon nanotubes and the nitric acid solution. The heating temperature can further be 135° C. to 140° C., and can be exemplarily 130° C., 132° C., 135° C., 138° C., or 140° C.

[0038] In some embodiments, the heating time in step S1 can be 10 hours to 12 hours, which is beneficial to further improve the pretreatment effect. The heating time can further be 10 hours to 11 hours, and can be 10 hours, 10.5 hours, 11 hours, 11.5 hours or 12 hours, etc.

[0039] In some embodiments, the drying temperature in step S1 can be 60° C. to 110° C., which is conducive to further effectively removing impurities and improving the purity of the open carbon nanotubes. The drying temperature can further be 60° C. to 90° C., and can be 60° C., 70° C., 80° C., 90° C., 100° C., or 110° C., for example.

[0040] In some embodiments, the drying time in step S1 may be 24 hours to 48 hours, further may be 24 hours to 36 hours, and illustratively may be 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours.

[0041] Step S2: placing the open carbon nanotubes in a container, and evacuating the container to a vacuum degree of 0.05 Pa to 0.1 Pa.

[0042] During this step, vacuuming the container causes the gas pressure inside to drop significantly, creating a significant pressure gradient. This pressure differential allows air and water vapor to be rapidly extracted, ensuring a clean interior. Furthermore, the open carbon nanotube cavities may also contain gaseous components, which are effectively removed by vacuuming, creating a near-vacuum environment for the subsequent injection of the metal catalyst solution.

[0043] In some embodiments, the temperature during vacuuming can be 60°C~80°C, which is conducive to further fully discharging the gas inside the open carbon nanotubes, avoiding the formation of bubbles or residual air inside the open carbon nanotubes, so that the catalyst solution in the subsequent steps can fully enter the cavity of the open carbon nanotubes.

[0044] Step S3: maintaining the above vacuum degree, injecting a metal catalyst solution into the container to impregnate the open carbon nanotubes to obtain a precursor mixture.

[0045] In this step, a metal catalyst solution is mixed with the open carbon nanotubes, and a negative pressure liquid phase method is used to rapidly allow the metal catalyst solution to enter the open carbon nanotubes. Specifically, under vacuum conditions, the pressure differential effectively propels the metal catalyst solution into the open carbon nanotubes, effectively increasing the degree of metal catalyst wetting. This facilitates the metal catalyst's entry into the carbon nanotubes and reduces the amount of metal catalyst used. Furthermore, the hollow interior of the open carbon nanotubes creates a larger surface area for the metal catalyst's reaction, allowing the metal ions in the metal catalyst solution to effectively contact the inner surface of the carbon nanotubes, thereby increasing the metal catalyst loading within a limited space.

[0046] In some embodiments, the metal catalyst solution and open carbon nanotubes can be stirred during the impregnation process to ensure uniform dispersion of the solution and better bind the metal ions to the carbon nanotubes, avoiding the formation of areas of localized excessive concentration and improving dispersion uniformity. The stirring time can be 3 to 5 hours, which is beneficial for further improving the impregnation effect and dispersibility of the metal catalyst solution. The impregnation and stirring time can further be 3 to 5 hours, and illustratively can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours.

[0047] In some embodiments, the metal catalyst solution may include at least one of CoCl2, Co(NO3)2, FeCl3, Fe(NO3)3, NiCl3, Ni(NO3)3, ZnCl2, and Zn(NO3)2. 2+ 、Fe 3+ 、Ni 2+ or Zn 2+ Metal ions can further catalyze the reduction / oxidation reaction of sulfur in lithium-sulfur batteries, improving the battery's charge and discharge efficiency; they can also reduce the accumulation of polysulfides on the electrode surface and increase the battery's cycle life; they also help adsorb lithium polysulfides on carbon nanotubes, reducing their dissolution in the electrolyte and inhibiting the shuttle effect.

[0048] In some embodiments, the concentration of the metal catalyst solution can be 1 g / L to 5 g / L. Because the metal catalyst enters the open carbon nanotubes, it effectively reduces deactivation caused by direct contact with polysulfides. Therefore, a lower metal catalyst solution can meet the requirements of high catalytic efficiency, thereby reducing the amount of catalyst used. The concentration of the metal catalyst solution can further be 1 g / L to 3 g / L, and illustratively can be 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, or 5 g / L.

[0049] In some embodiments, the mass ratio of the metal catalyst solution to the open-ended carbon nanotubes in the precursor mixture can be (0.1-0.5):1. A lower metal catalyst solution content can meet the requirements for efficient catalysis, which helps save costs. The mass ratio of the metal catalyst solution to the open-ended carbon nanotubes can further be (0.1-0.3):1, and illustratively can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, or 0.5:1.

[0050] In some embodiments, the purity of the carbon nanotubes can be less than 99%, that is, the purity of the open-ended carbon nanotubes can also be less than 99%. For example, commercial carbon nanotubes with a purity of less than 99% can be used. Since such materials contain trace amounts of metal catalysts during the production process, they can be used as the carbon nanotubes in the embodiments of this application, further reducing the use of metal catalysts.

[0051] Step S4: drying and heat-treating the precursor mixture to obtain a carbon nanotube composite material.

[0052] In this step, the precursor mixture is filtered and dried to remove external solutions and impurities to obtain a clean solid product. The solid product is then heat-treated to convert the metal ions in the metal catalyst solution into metal particles such as metal elements, metal compounds or alloys. The metal particle catalyst is coated inside the carbon nanotubes, thereby obtaining a composite material of carbon-coated metal particles.

[0053] Both carbon nanotubes and metal particles possess excellent electrical conductivity, forming a conductive framework that helps improve the conductivity of the cathode material. Understandably, a small amount of metal particles will also adhere to the outer surface of the carbon nanotubes. This can increase the metal particle loading rate while having a smaller impact on catalytic efficiency. Residual metal particles on the surface of the carbon nanotube composite can also be reduced by appropriately increasing the number of filtration and cleaning cycles.

[0054] Metal catalysts can effectively promote the adsorption of positive electrode materials and the rapid catalytic conversion of polysulfides, thereby reducing the shuttle effect in lithium-sulfur batteries and improving sulfur utilization, thereby increasing the coulombic efficiency and cycle life of the prepared lithium-sulfur batteries. At the same time, because the metal particles are coated inside the carbon nanotubes, the risk of direct contact between the metal particles and polysulfides, resulting in the loss of catalytic activity due to sulfurization, can be reduced, which is beneficial to improving the catalytic activity and stability of the metal particles, thereby reducing the shuttle effect of polysulfides, increasing the utilization rate of sulfur active substances, and improving the capacity and cycle stability of lithium-sulfur batteries. In addition, the barrier of carbon nanotubes also weakens the strong adsorption of metal particles and polysulfides, releasing the active catalytic sites of the metal catalyst, which is conducive to the efficient and long-term catalytic reaction.

[0055] In some embodiments, in step S4, the heat treatment temperature may be 400°C to 800°C, which is beneficial for reducing the metal ions in the metal catalyst solution to form metal particles, further promoting the crystallization process of the metal particles, and improving the particle size and uniformity of the metal particles. The heat treatment temperature may further be 600°C to 800°C, and may be 400°C, 500°C, 600°C, 700°C, or 800°C, for example.

[0056] In some embodiments, in step S4, the heat treatment time can be 2 hours to 3 hours, which is conducive to further improving the crystallization effect of the metal particles. The heat treatment time can further be 2.5 hours to 3 hours, and can be 2 hours, 2.2 hours, 2.5 hours, 2.6 hours, 2.8 hours, or 3 hours, for example.

[0057] In some embodiments, the metal particles may have a particle size of 2 nm to 10 nm. A smaller particle size facilitates dispersion within the carbon nanotubes, while providing a larger specific surface area, further improving catalytic efficiency. The metal particles may further have a particle size of 2 nm to 5 nm, illustratively 2 nm, 3 nm, 4 nm, 5 nm, 7 nm, 8 nm, or 10 nm.

[0058] Step S5: adding sulfur to the carbon nanotube composite material, grinding and heating to obtain a positive electrode material.

[0059] Specifically, the carbon nanotube composite material and sulfur were mixed in a mass ratio of (3:7) to (2:8), ground for 30 min to 60 min, and then heat treated at 155°C to 155°C in an inert atmosphere for 10 h to 12 h to obtain a positive electrode material for lithium-sulfur batteries with carbon nanotube-coated metal particles.

[0060] In some embodiments, the commercial carbon nanotubes with a purity lower than 99% described in step S3 can also be directly used as the carbon nanotube composite material in the embodiments of the present application, and loaded with sulfur to prepare a positive electrode material, because they contain trace metal catalysts inside.

[0061] Compared with the prior art, the preparation method of the positive electrode material provided in the embodiment of the present application has the following beneficial effects:

[0062] 1. This application utilizes a negative pressure liquid phase method to fill the interior of carbon nanotubes with a metal catalyst solution, reducing the concentration and dosage of the metal catalyst and shortening the time required to impregnate the carbon nanotubes. This achieves efficient filling with a low metal catalyst dosage. Furthermore, the metal catalyst content in the cathode material is low, reducing production costs while improving catalytic activity and efficiency.

[0063] 2. The structure of the carbon nanotube-encapsulated metal particle catalyst improves the conductivity of the cathode material. The catalyst is also encapsulated within the carbon nanotubes, reducing deactivation caused by direct contact between the catalyst and polysulfides. It also weakens the strong adsorption of polysulfides, releasing the catalyst's active catalytic sites and ensuring a long-lasting and stable catalytic effect.

[0064] 3. The preparation method of the present application has simple process and low cost, which is conducive to the large-scale production of lithium-sulfur batteries.

[0065] The present invention provides a positive electrode material prepared using the aforementioned positive electrode material preparation method. The positive electrode material comprises carbon nanotubes, metal particles, and sulfur supported on the carbon nanotubes. The metal particles are located within the carbon nanotubes, providing a highly efficient catalytic effect that effectively reduces the shuttle effect in lithium-sulfur batteries while also improving the longevity and stability of the positive electrode material.

[0066] In some embodiments, the mass percentage of metal particles and open carbon nanotubes in the positive electrode material can be 1 wt% to 2.5 wt%. A trace amount of metal particle catalyst can achieve long-term and stable operation of the lithium-sulfur battery. The mass percentage of metal particles and carbon nanotubes can further be 1.5 wt% to 2.5 wt%, and can be 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, or 2.5 wt%, etc.

[0067] An embodiment of the present application provides a lithium-sulfur battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet includes the aforementioned positive electrode material.

[0068] Compared with the prior art, the lithium-sulfur battery provided in the embodiment of the present application adopts the aforementioned positive electrode material, which reduces the shuttle effect of polysulfides in the lithium-sulfur battery and effectively improves the capacity, cycle performance and stability of the lithium-sulfur battery.

[0069] The above-mentioned positive electrode material and its preparation method are further described below through specific examples.

[0070] Example 1

[0071] Step 1: Dissolve 2 g of carbon nanotube array powder in 100 mL of concentrated nitric acid solution (concentration: 10 mol / L), heat at 140°C for 10 h, filter, and dry at 110°C for 24 h to obtain open carbon nanotubes.

[0072] Step 2: Place 100 mg of open carbon nanotubes in a round-bottom flask, evacuate for 0.5 h to a vacuum degree of 0.1 Pa, and heat in a water bath at 80° C. while evacuating.

[0073] Step 3: Maintaining the vacuum, stop heating, and after cooling to room temperature, inject 20 mL of a 50 g / L ethanol solution of Fe(NO3)3 metal catalyst into the container using a syringe to impregnate the open carbon nanotubes. Stir for 5 hours to obtain a precursor mixture. To maintain the vacuum environment, do not remove the syringe after injecting the liquid.

[0074] Step 4: Rinse and filter the precursor mixture with ethanol, wash off the external solution and dry it to obtain a solid product. The solid product is heat-treated at a rate of 5°C / min to 450°C under an argon atmosphere for 3 hours to obtain a composite material of carbon-coated metal particles with an Fe2O3 content of 2wt%.

[0075] Step 5: Evenly mix the above composite material and sulfur powder in a mass ratio of 3:7, grind for 30 minutes, and keep warm at 155°C for 12 hours in argon protective gas to obtain a positive electrode material in which metal particles Fe2O3 are coated inside carbon nanotubes and the mass percentage of metal particles Fe2O3 and carbon nanotubes is 2wt%.

[0076] Example 2

[0077] The specific process of the preparation process refers to Example 1. The difference from Example 1 is that the heat treatment temperature in step 4 is 800°C, and the metal particles Fe3C are coated inside the carbon nanotubes, and the mass percentage of the metal particles Fe3C and the carbon nanotubes is 2wt% of the positive electrode material. The preparation method of the remaining positive electrode materials is basically the same as that in Example 1 and will not be described in detail here.

[0078] Example 3

[0079] The specific process of the preparation process refers to Example 1, and the difference from Example 1 is that the metal catalyst solution in step 3 is a CoCl2 solution; the heat treatment temperature in step 4 is 800°C, and the metal particles Co are coated inside the carbon nanotubes, and the mass percentage of the metal particles Co and the carbon nanotubes is 2wt% of the positive electrode material. The preparation method of the remaining positive electrode materials is basically the same as that in Example 1, and will not be described in detail here.

[0080] Comparative Example 1

[0081] The specific process of the preparation process refers to Example 1. The difference from Example 1 is that no Fe(NO3)3 metal catalyst is added in step 3, and only ethanol solution is used for impregnation to obtain a positive electrode material without metal particles. The preparation method of the remaining positive electrode materials is basically the same as that in Example 1 and will not be described in detail here.

[0082] Comparative Example 2

[0083] The specific process of the preparation process refers to Example 1. The difference from Example 1 is that: no vacuum treatment is performed in step 2, metal particles Fe2O3 are loaded on the outside of the carbon nanotubes, and the positive electrode material of the metal particles Fe2O3 and carbon nanotubes with a mass percentage of 2wt% is prepared. The preparation method of the remaining positive electrode materials is basically the same as that in Example 1 and will not be elaborated here.

[0084] The following tests were performed on the positive electrode materials obtained in Examples 1-3 and Comparative Examples 1-2, and corresponding test results were obtained.

[0085] 1. The electrical properties of the positive electrode materials obtained in Examples 1-3 and Comparative Examples 1-2 were tested. The results are shown in Table 1.

[0086] The specific test methods are as follows:

[0087] Electrical performance test: The positive electrode materials in Examples 1-3 and Comparative Examples 1-2 were uniformly mixed with the binder PVDF and the conductive carbon nanotubes in a mass ratio of 7:2:1 in N-methylpyrrolidone (NMP) solvent, stirred thoroughly to form a slurry, and then coated on the current collector and dried in an oven at 60°C. Finally, the positive electrode sheets were punched out for use. The sulfur loading in the positive electrode sheets was 1 mg / cm 2 Next, in an argon-filled glove box, the button cell was assembled in the following order: positive electrode casing, gasket, positive electrode sheet, electrolyte, separator, electrolyte, lithium sheet, gasket, spring, and negative electrode casing. Ensure that 20 μL / mg of electrolyte was added to both sides of the separator. During assembly, the positive electrode casing was placed on the bottom and the negative electrode casing on the top. A button cell sealer was used to compact the lithium-sulfur battery in preparation for testing.

[0088] The test conditions were 25°C, the charge and discharge current was set to 0.5C, the charge and discharge voltage range was 1.7V~2.8V, and 100 cycle tests were performed.

[0089]

[0090] As can be seen from Table 1, the positive electrode materials of Examples 1-3 all have good initial discharge capacity and cycle retention rates. Among them, the cycle retention rates of the positive electrode materials of Examples 1-3 are relatively high, all at 90% or above, with the highest being 93%, significantly higher than the cycle retention rates of Comparative Example 1 (70%) and Comparative Example 2 (75%). This demonstrates that the positive electrode materials of Examples 1-3 of the present application, prepared using a negative pressure liquid phase method with carbon nanotube-coated metal particle catalysts, can significantly improve cycle performance while maintaining a high initial discharge capacity, thereby enhancing the battery's longevity and stability.

[0091] The positive electrode materials prepared in Example 1 and Comparative Example 1 were prepared by referring to the above positive electrode sheet and battery preparation methods, and the sulfur loading in the positive electrode sheet was changed to 2 mg / cm 2 The electrolyte content is 5μL / mg, and the charge and discharge test is carried out at a discharge current of 0.1C. The results are as follows Figure 2 As shown. It shows that when the sulfur loading is 2 mg / cm 2 When the content of the lean electrolyte is low and the current is 0.03C, the first cycle discharge capacity of the battery prepared in Example 1 is 1350mAh / g, while that in Comparative Example 1 is only 1230mAh / g.

[0092] The cathode materials prepared in Example 1 and Comparative Example 1 were prepared by referring to the above cathode sheet and battery preparation methods, and the sulfur loading in the cathode sheet was changed to 3.5 mg / cm 2 The electrolyte content is 5μL / mg, and the charge and discharge test is carried out at a discharge current of 0.1C. The results are as follows Figure 3 It shows that under the conditions of high sulfur loading and lean electrolyte, compared with Comparative Example 1, the initial capacity of the battery prepared in Example 1 reaches 900 mAh / g, and can be stably cycled for more than 100 cycles, with excellent specific capacity and cycle performance.

[0093] 2. The positive electrode material obtained in Example 1 was observed by transmission electron microscopy. The results are as follows: Figure 4 As shown, the positive electrode material obtained in Example 1 was subjected to thermogravimetric testing in air, and the results were as follows: Figure 5 shown.

[0094] By observation Figure 4 It can be seen that the particle size of the metal particles in Example 1 is about 5 nm, and the metal particles are located inside the carbon nanotube lumen with good dispersion and uniformity.

[0095] Figure 5 The weight loss peak at 400℃~600℃ represents the combustion of carbon (carbon nanotubes) in air. The results show that the content of metal catalyst in the positive electrode material of Example 1 is 2wt%, which is significantly lower than that of traditional lithium-sulfur positive electrode materials. In the examples of this application, the high catalytic performance of the positive electrode material is achieved with a lower catalyst content, which saves costs and is efficient and stable.

[0096] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: include: pre-treating the carbon nanotubes to obtain open carbon nanotubes; Placing the open carbon nanotubes in a container, and evacuating the container to a vacuum degree of 0.05 Pa to 0.1 Pa; maintaining the vacuum degree, injecting a metal catalyst solution into the container to impregnate the open carbon nanotubes to obtain a precursor mixture; drying and heat-treating the precursor mixture to convert the metal catalyst into metal particles that fill the interior of the open carbon nanotubes, thereby obtaining a carbon nanotube composite material; as well as Sulfur is added to the carbon nanotube composite material, followed by grinding and heating to obtain the positive electrode material.

2. The method for preparing the positive electrode material according to claim 1, wherein: The carbon nanotubes are aligned carbon nanotubes, and the aligned carbon nanotubes include at least one of carbon nanotube arrays, aligned multi-walled carbon nanotubes, and aligned double-walled carbon nanotubes; and / or The purity of the carbon nanotubes is lower than 99%.

3. The method for preparing the positive electrode material according to claim 1, wherein: The metal catalyst solution comprises at least one of CoCl2, Co(NO3)2, FeCl3, Fe(NO3)3, NiCl3, Ni(NO3)3, ZnCl2 and Zn(NO3)2; and / or The concentration of the metal catalyst solution is 1 g / L to 5 g / L.

4. The method for preparing the positive electrode material according to claim 1, wherein: In the precursor mixture, the mass ratio of the metal catalyst solution to the open carbon nanotubes is (0.1-0.5):

1.

5. The method for preparing the positive electrode material according to claim 1, wherein: The step of impregnating the open carbon nanotubes with the metal catalyst solution further includes: The metal catalyst solution and the open carbon nanotubes are stirred for 3 to 5 hours.

6. The method for preparing the positive electrode material according to claim 1, wherein: When the container is vacuumed, the temperature inside the container is 60° C. to 80° C.

7. The method for preparing the positive electrode material according to claim 1, wherein: In the heat treatment step, the heat treatment temperature is 400° C. to 800° C., and the heat treatment time is 3 h to 5 h.

8. A positive electrode material, characterized in that Prepared by the preparation method of the positive electrode material according to any one of claims 1 to 7, the positive electrode material includes a carbon nanotube composite material and sulfur loaded on the carbon nanotube composite material, wherein the carbon nanotube composite material includes open carbon nanotubes and metal particles located inside the open carbon nanotubes.

9. The positive electrode material according to claim 8, characterized in that In the positive electrode material, the mass percentage of the metal particles and the open carbon nanotubes is 1 wt % to 2.5 wt %.

10. A lithium-sulfur battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet comprises the positive electrode material according to any one of claims 8 to 9.

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