Composite cathode material, preparation method thereof, lithium-sulfur battery cathode sheet and lithium-sulfur battery

Abstract

The embodiment of the application provides a kind of composite positive material and its preparation method, lithium-sulfur battery positive sheet and lithium-sulfur battery.The composite positive material includes porous carbon matrix, metal atom and carbon nanotube, carbon nanotube is in situ grown on the metal atom attached to the pore and surface of porous carbon matrix, and N element is introduced in the growth process of carbon nanotube.The application is in situ grown by carbon nanotube on porous carbon skeleton and then adjusts the pore structure of porous composite material, effectively inhibits the shuttle effect of polysulfide.At the same time, nitrogen doping helps to increase the chemical adsorption capacity of polysulfide, and also effectively inhibits the shuttle effect of polysulfide, thereby improving the utilization rate of sulfur and the cycle life of battery.The preparation method of nanotube composite material for inhibiting the shuttle effect of lithium polysulfide in the prior art is complex and has high cost.

Description

Technical Field

[0001] The present invention relates to the field of lithium-sulfur batteries, specifically to a composite cathode material and its preparation method, a lithium-sulfur battery cathode sheet, and a lithium-sulfur battery. Background Technology

[0002] With the rapid development of emerging applications such as electric vehicles, portable electronic devices, and renewable energy storage systems, researchers are dedicated to developing electrochemical energy storage systems with high energy density, excellent stability, and high cost-effectiveness. Traditional lithium-ion batteries can no longer meet these demands, and the research and exploration of novel battery systems are receiving widespread attention. Among them, lithium-sulfur batteries stand out due to their extremely high theoretical energy density (2600 Wh·kg⁻¹). -1 With its advantages of low cost, lithium-sulfur batteries are considered an ideal candidate system for overcoming the performance bottleneck of lithium-ion batteries. Its cathode active material, elemental sulfur, is abundant, inexpensive, and non-toxic. Furthermore, the electrochemical reaction of lithium-sulfur batteries is based on the reversible reaction of sulfur with lithium sulfide, which does not rely on scarce metal resources and aligns with the core concept of sustainable development.

[0003] Despite the numerous advantages of lithium-sulfur batteries, many challenges in practical applications severely hinder their commercialization. To address these issues, researchers are attempting to synthesize carbon materials that can physically suppress lithium polysulfide shuttle, improve the low conductivity of sulfur, and alleviate cathode volume expansion. In particular, three-dimensional porous carbon materials possess high specific surface area, tunable pore structure, and excellent conductivity, enabling them not only to physically adsorb polysulfides but also to provide continuous electron transport pathways. However, single three-dimensional porous carbon materials still face problems such as polysulfide desorption and localized failure of the conductive network during long-term cycling. To address this challenge, carbon nanotubes, due to their one-dimensional conductivity, high crystallinity, and abundant surface active sites, have become an ideal choice for reinforcing carbon-based materials.

[0004] However, although existing studies have explored the applications of carbon nanotube composites, the preparation methods (such as arc discharge, laser ablation, and chemical vapor deposition) are complex and costly, which limits their large-scale application.

[0005] Therefore, there is an urgent need to develop a method for large-scale preparation of carbon nanotube composite materials, so as to effectively improve the poor cycle performance of lithium-sulfur batteries caused by the lithium polysulfide shuttle effect. Summary of the Invention

[0006] This application provides a composite cathode material and its preparation method, a lithium-sulfur battery cathode sheet, and a lithium-sulfur battery, to at least solve the problems of complexity and high cost in the preparation methods of nanotube composite materials for suppressing the lithium polysulfide shuttle effect in the prior art.

[0007] According to one aspect of the embodiments of this application, a composite cathode material is provided. The composite cathode material includes a porous carbon matrix, metal atoms and carbon nanotubes. The metal atoms are randomly distributed in the pores and surface of the porous carbon matrix. The carbon nanotubes are grown in situ in the pores and surface of the porous carbon matrix using metal atoms as catalysts. N atoms are introduced during the growth process of the carbon nanotubes.

[0008] In several embodiments, the mass ratio of carbon nanotubes to porous carbon matrix is ​​1–5:19, and the specific surface area of ​​the porous carbon matrix is ​​169–253.7 m². 2 ·g -1 The pore size of the porous carbon matrix is ​​≤160nm.

[0009] In several embodiments, the metal atoms are selected from any one or more of cobalt atoms, iron atoms, and nickel atoms, and the mass percentage of the metal atoms in the composite cathode material is 1% to 5%.

[0010] According to another aspect of the embodiments of this application, a method for preparing the aforementioned composite cathode material is provided, comprising: step S1, heating and stirring raw materials including an organic carbon source, a soluble salt template and water to obtain a mixed solution; step S2, stirring and mixing raw materials including the mixed solution and a metal salt catalyst and then freeze-drying to obtain a precursor dry gel; step S3, performing a first carbonization treatment on the precursor dry gel in a first inert atmosphere to form a porous carbon framework; step S4, sequentially grinding, washing and drying the porous carbon framework to obtain a hierarchical porous carbon support; step S5, performing a second carbonization treatment on raw materials including the hierarchical porous carbon support and a nitrogen-containing carbon source in a second inert atmosphere to obtain the composite cathode material; wherein, the first carbonization treatment process includes a first-stage carbonization treatment and a second-stage carbonization treatment performed sequentially, and the temperature of the second-stage carbonization treatment is higher than the temperature of the first-stage carbonization treatment.

[0011] In several embodiments, step S1 satisfies at least one of the following conditions: (1) the organic carbon source is selected from any one or more of natural high molecular weight starch, cotton, and soybean; (2) the soluble salt template is selected from any one or more of sodium chloride, magnesium chloride, and calcium chloride; (3) the heating and stirring speed is 300~500 rpm; (4) the heating and stirring time is 0.1~0.5 h; (5) the heating and stirring temperature is 45~60℃.

[0012] In several embodiments, step S2 satisfies at least one of the following conditions: (1) the metal salt catalyst is selected from any one or more of cobalt acetate tetrahydrate, cobalt sulfate, cobalt nitrate, and cobalt chloride; (2) the freeze-drying temperature is -20~35℃; (3) the freeze-drying time is 12~16 h; (4) the stirring speed is 500~800 rpm; (5) the stirring time is 0.5~1 h.

[0013] In several embodiments, the preparation method satisfies at least one of the following conditions: (1) the first inert atmosphere is selected from any one or more of Ar and N2; (2) the primary carbonization process includes: at 1~3℃·min -1 The heating rate is from room temperature to 200~300℃ and held for 60~120 min; the secondary carbonization process includes: heating at 3~5℃·min -1 The heating rate is increased from 200~300℃ to 500~600℃ and kept at that temperature for 60~120min; (3) The drying temperature is 40~50℃ and the drying time is 6~12h.

[0014] In several embodiments, step S5 satisfies at least one of the following conditions: (1) the second carbonization process includes: at 3~5℃·min -1 The heating rate is from room temperature to 800℃ and held for 300~360min; (2) The mass ratio of the hierarchical porous carbon support to the nitrogen-containing carbon source is 1:5~25; (3) The nitrogen-containing carbon source is selected from any one or more of dihydrodiamine and melamine; (4) The average particle size of the composite cathode material is 56~124nm; (5) The first inert atmosphere is selected from any one or more of Ar and N2.

[0015] According to another aspect of the embodiments of this application, a lithium-sulfur battery cathode sheet is provided, including a cathode material, wherein the cathode material is the aforementioned composite cathode material or is prepared by the aforementioned preparation method.

[0016] According to another aspect of the embodiments of this application, a lithium-sulfur battery is provided, including a positive electrode and a negative electrode, wherein the positive electrode is the aforementioned lithium-sulfur battery positive electrode.

[0017] In this embodiment, the presence of metal atoms promotes the redox reaction of polysulfides, accelerating the electrochemical process and effectively improving the conductivity of lithium-sulfur batteries. Carbon nanotubes are grown in situ on a porous carbon support, and the growth of carbon nanotubes does not destroy the main structure of the porous carbon material, but rather forms a composite structure with it. The three-dimensional conductive network formed by the cross-linking of carbon nanotubes can effectively adsorb polysulfides and suppress the shuttle effect. Simultaneously, the doping of nitrogen atoms helps increase the chemisorption capacity of polysulfides, effectively suppressing the shuttle effect of polysulfides, thereby improving the cycle stability of the battery. Furthermore, the introduced highly crystalline carbon nanotubes provide a fast channel for electron transport, thereby improving the electrochemical reaction kinetics of sulfur species. Finally, through the synergistic effect of carbon nanotubes and porous carbon in the composite material, the shuttle phenomenon of polysulfides can be suppressed more efficiently, while providing a fast transport channel for ions and electrons. This is beneficial for improving the cycle stability of lithium-sulfur batteries and exhibiting high charge-discharge capacity. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0019] Figure 1 This is a process flow diagram of a composite cathode material preparation according to the present application;

[0020] Figure 2 These are SEM images of Co-HPC-CNT-15 prepared according to Example 1 of this application and Co-HPC prepared according to Comparative Example 1;

[0021] Figure 3 The images show the XRD patterns of Co-HPC-CNT-15 prepared according to Example 1 of this application and Co-HPC prepared according to Comparative Example 1.

[0022] Figure 4 These are XPS images of Co-HPC-CNT-15 prepared according to Example 1 of this application and Co-HPC prepared according to Comparative Example 1. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0024] As described in the background section, existing methods for preparing nanotube composite materials to suppress the lithium polysulfide shuttle effect are complex and costly. To address these issues, this application provides a composite cathode material comprising a porous carbon matrix, metal atoms, and carbon nanotubes. The metal atoms are attached to the pores and surface of the porous carbon matrix, and the carbon nanotubes are grown in situ within the pores and surface of the porous carbon matrix. Both the carbon nanotubes and the porous carbon matrix are doped with nitrogen atoms.

[0025] Carbon nanotubes are grown in situ on a porous carbon support, and the growth of carbon nanotubes does not destroy the main structure of the porous carbon material, but rather forms a composite structure with it. The three-dimensional conductive network formed by the cross-linking of carbon nanotubes can effectively adsorb polysulfides and suppress the shuttle effect. At the same time, nitrogen doping helps to increase the chemisorption capacity of polysulfides, effectively suppressing the polysulfide shuttle effect, thereby improving the cycle stability of the battery. In addition, the introduced highly crystalline carbon nanotubes can provide a fast channel for electron transport, thereby improving the electrochemical reaction kinetics of sulfur species. Finally, through the synergistic effect of carbon nanotubes and porous carbon in the composite material, the shuttle phenomenon of polysulfides can be suppressed more efficiently, while providing a fast transport channel for ions and electrons. This is beneficial to improving the cycle stability of lithium-sulfur batteries and exhibiting high charge-discharge capacity.

[0026] In several embodiments, the mass ratio of carbon nanotubes to porous carbon matrix is ​​1–5:19, and the specific surface area of ​​the porous carbon matrix is ​​169–253.7 m². 2 ·g -1 The pore size in the porous carbon matrix is ​​≤160nm.

[0027] Optimizing the mass ratio of carbon nanotubes to porous carbon matrix within the above range ensures a dense and uniform distribution of carbon nanotubes on the porous carbon framework, effectively enhancing the material's conductive network while reducing the risk of excessive carbon nanotube accumulation leading to pore blockage and impacting ion transport in lithium-sulfur batteries. Controlling the specific surface area of ​​the porous carbon matrix within the above range also provides more active sites, enhancing the physical adsorption capacity for polysulfides.

[0028] In several embodiments, the metal atoms are selected from any one or more of cobalt atoms, iron atoms, and nickel atoms, and the mass percentage of the metal atoms in the composite cathode material is 1% to 5%.

[0029] Optimizing the mass percentage of metal atoms in the composite cathode material is beneficial for enhancing the catalytic activity and electron transport capability of the material. Cobalt atoms, as an effective catalyst, can promote the conversion reaction of polysulfides, accelerate electron transfer, and thus significantly improve the overall electrochemical performance of lithium-sulfur batteries. Attaching metal atoms to the pores and surface of the porous carbon matrix not only increases the number of active sites but also enhances the structural stability of the composite material, helping to maintain electrode integrity under long-term cycling. Further, the mass percentage of metal atoms in the composite cathode material is preferably 1% to 2%.

[0030] According to another aspect of the embodiments of this application, a method for preparing the aforementioned composite cathode material is provided, comprising: step S1, heating and stirring raw materials including an organic carbon source, a soluble salt template and water to obtain a mixed solution; step S2, stirring and mixing raw materials including the mixed solution and a metal salt catalyst and then freeze-drying to obtain a precursor dry gel; step S3, performing a first carbonization treatment on the precursor dry gel in a first inert atmosphere to form a porous carbon framework; step S4, sequentially grinding, washing and drying the porous carbon framework to obtain a hierarchical porous carbon support; step S5, performing a second carbonization treatment on raw materials including the hierarchical porous carbon support and a nitrogen-containing carbon source in a second inert atmosphere to obtain the composite cathode material; wherein, the first carbonization treatment process includes a first-stage carbonization treatment and a second-stage carbonization treatment performed sequentially, and the temperature of the second-stage carbonization treatment is higher than the temperature of the first-stage carbonization treatment.

[0031] The above method effectively solves the problems of slow electrochemical reaction kinetics and polysulfide shuttle effect in the sulfur cathode of lithium-sulfur batteries by in-situ growth of carbon nanotubes on a porous carbon framework combined with nitrogen doping. The technical principle is as follows: a porous carbon framework is first prepared using an organic carbon source, a soluble salt template, and a metal salt catalyst. During this process, the volatilization of the soluble salt template forms a porous structure, while cobalt particles are fixed in the first carbonization treatment, providing a catalyst for the subsequent growth of carbon nanotubes. In the second carbonization stage, dihydrodiamine is used as the carbon source for growing carbon nanotubes. Under an inert atmosphere and high temperature decomposition, the carbon produced grows in situ on the surface of the porous carbon framework under the action of the cobalt catalyst, forming carbon nanotubes, while simultaneously achieving nitrogen doping of the carbon material. The highly crystalline one-dimensional carbon nanotubes not only provide a continuous electron transport path but also work synergistically with the porous carbon framework to physically adsorb and chemically fix polysulfides, inhibiting their shuttle effect and improving sulfur utilization. Nitrogen doping enhances the chemical adsorption capacity of the carbon material for polysulfides, further improving the electrochemical performance of the cathode material. Therefore, the composite cathode material obtained by the above preparation method can significantly improve the cycle stability and charge / discharge efficiency of lithium-sulfur batteries, providing an effective approach for the development of high-energy-density and long-life energy storage devices. Furthermore, the above preparation method is simple and has lower cost.

[0032] In several embodiments, step S1 satisfies at least one of the following conditions: (1) the organic carbon source is selected from any one or more of natural high molecular weight starch, cotton, and soybean; (2) the soluble salt template is selected from any one or more of sodium chloride, magnesium chloride, and calcium chloride; (3) the heating and stirring speed is 300~500 rpm; (4) the heating and stirring time is 0.1~0.5 h; (5) the heating and stirring temperature is 45~60 ℃.

[0033] First, the selected organic carbon sources can be transformed into carbon materials with good conductivity and stability during heat treatment. Second, the soluble salt templates are removed during carbonization, leaving a three-dimensional porous structure, which helps improve the electrochemical performance of the material. Third, heating and stirring the mixed solution helps to uniformly disperse the precursor components, thereby promoting more efficient carbonization and nitrogen doping reactions. Finally, by controlling the temperature and time of the carbonization treatment within the above ranges, especially in the second carbonization, the carbon source generated by the decomposition of dihydrodiamine at high temperature, under the action of a cobalt metal catalyst, grows carbon nanotubes in situ on the pore surface of the porous carbon, constructing an efficient electron transport pathway. Simultaneously, the incorporation of nitrogen enhances the polysulfide adsorption capacity of the material. Through the synergistic effect of the above parameters, nitrogen-doped carbon nanotubes and porous carbon form a composite structure. This three-dimensional conductive network can significantly suppress the shuttle effect of polysulfides in lithium-sulfur batteries, improve the electrochemical reaction kinetics of sulfur species, and enhance the cycle stability and charge / discharge capacity of the battery. This not only reduces production costs but also provides greater flexibility and controllability.

[0034] In several embodiments, step S2 satisfies at least one of the following conditions: (1) the metal salt catalyst is selected from any one or more of cobalt acetate tetrahydrate, cobalt sulfate, cobalt nitrate, and cobalt chloride; (2) the freeze-drying temperature is -20 to 35 °C; (3) the freeze-drying time is 12 to 16 h; (4) the stirring speed is 500 to 800 rpm; and (5) the stirring time is 0.5 to 1 h.

[0035] The preferred metal salt catalysts decompose and generate cobalt particles during subsequent heat treatment, thereby promoting the in-situ growth of carbon nanotubes from a nitrogen-containing carbon source on a hierarchical porous carbon support under high-temperature carbonization conditions. Freeze-drying helps form a stable precursor dry gel structure, ensuring uniform distribution of the metal salts and preventing their aggregation during subsequent processing. By controlling the drying conditions, the retention of the porous structure and the integrity of the crystal morphology are enhanced.

[0036] In several embodiments, the preparation method satisfies at least one of the following conditions: (1) the first inert atmosphere is selected from any one or more of Ar and N2; (2) the primary carbonization process includes: at 1~3℃·min-1 The heating rate is from room temperature to 200~300℃ and held for 60~120 min; the secondary carbonization process includes: heating at 3~5℃·min -1 The heating rate is increased from 200~300℃ to 500~600℃ and kept at that temperature for 60~120min; (3) The drying temperature is 40~50℃ and the drying time is 6~12h.

[0037] In the preparation of cathode materials, carbonization under an inert atmosphere helps protect the material from oxidation at high temperatures while promoting the effective reaction between the metal catalyst and the carbon source, forming a highly crystalline carbon nanotube structure. The first carbonization process, through multi-stage heating and holding, achieves the decomposition of metal salts and the formation of a preliminary porous carbon framework. Optimal temperature control facilitates the uniform distribution of metal particles and the construction of the porous structure. Subsequent drying ensures the structural stability and pore clarity of the material after template removal. Optimized drying conditions reduce potential structural damage caused by residual moisture during processing. This combination of optimized parameters results in a cathode material with not only a high specific surface area and a hierarchical porous structure but also high-efficiency growth of nitrogen doping and carbon nanotubes, forming a synergistic composite structure. In lithium-sulfur batteries, this composite structure effectively adsorbs and stabilizes polysulfides, significantly reducing their shuttle effect, while providing efficient electron and ion transport pathways, greatly improving the electrochemical performance and cycle stability of the cathode material.

[0038] In several embodiments, step S5 satisfies at least one of the following conditions: (1) the second carbonization process includes: at 3~5℃·min -1The heating rate is from room temperature to 800℃ and held for 300~360 min; (2) the mass ratio of hierarchical porous carbon support to nitrogen-containing carbon source is 1:5~25; (3) the nitrogen-containing carbon source is selected from any one or more of dihydrodiamine and melamine; (4) the average particle size of the composite cathode material is 56~124 nm; (5) the first inert atmosphere is selected from any one or more of Ar and N2. The above-mentioned heating program for the second carbonization treatment not only promotes the growth of carbon nanotubes, but also realizes the nitrogen doping of carbon materials. This is mainly due to the decomposition of the nitrogen-containing carbon source - dihydrodiamine and the presence of the cobalt catalyst. Dihydrodiamine, as the carbon source for growing carbon nanotubes, realizes the nitrogen doping of carbon materials at the same time, which is beneficial to enhance its chemical adsorption capacity for polysulfides and improve the electrochemical performance of lithium-sulfur batteries. At the same time, by controlling the mass ratio of nitrogen-containing carbon source to hierarchical porous carbon support within the above range, the growth of carbon nanotubes can be optimized to form a three-dimensional conductive network. The preferred carbonization process, performed under an inert atmosphere, provides a stable inert environment for carbon nanotube growth and nitrogen doping, which helps maintain the structural integrity and performance stability of the material. The preferred hierarchical porous carbon support, with an average particle size within the above range, helps provide sufficient space for carbon nanotube growth.

[0039] According to another aspect of the embodiments of this application, a lithium-sulfur battery cathode sheet is provided, including a cathode material, wherein the cathode material is the aforementioned composite cathode material or is prepared by the aforementioned preparation method.

[0040] The core of the lithium-sulfur battery cathode lies in the use of a composite cathode material consisting of nitrogen-doped carbon nanotubes loaded with cobalt metal. The lithium-sulfur battery cathode using this technology exhibits high energy density, excellent cycle stability, and high charge / discharge capacity. In applications such as electric vehicles and portable electronic devices, this composite cathode material can meet the demands for high energy density and long-life batteries.

[0041] According to another aspect of the embodiments of this application, a lithium-sulfur battery is provided, including a positive electrode and a negative electrode, wherein the positive electrode is the aforementioned lithium-sulfur battery positive electrode.

[0042] Lithium-sulfur batteries containing the above-mentioned lithium-sulfur battery cathode sheets have excellent high energy density and long lifespan.

[0043] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0044] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0045] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0046] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0047] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0048] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0049] Example 1

[0050] according to Figure 1 The method for preparing the composite cathode material shown is as follows:

[0051] Step (1): Weigh 1 g of starch and 3 g of NaCl and add them to 10 mL of deionized water. Place the mixture in a water bath at 60°C and stir for 4 hours to obtain a homogeneous starch solution. Add 500 mg of cobalt acetate tetrahydrate to the above solution and continue stirring until the metal salt is completely dissolved. Subsequently, freeze-dry the resulting solution to fix the catalyst particles and prevent their aggregation, and to allow the NaCl template to recrystallize to form a bulk dry gel.

[0052] Step (2): The above-mentioned dry gel was placed in a tube furnace and subjected to the first carbonization treatment under an argon atmosphere: the temperature was increased from room temperature to 200°C at a rate of 3°C / min and held for 60 minutes, and then increased from 200°C to 500°C at a rate of 3°C / min and held for 120 minutes. This process decomposed cobalt acetate tetrahydrate to generate metallic cobalt particles and form a porous carbon matrix;

[0053] Step (3): Grind the sample from step (2) for 10 minutes and wash it several times with deionized water to completely remove the NaCl template. Finally, dry the washed sample in a forced-air drying oven at 50°C for 12 hours to obtain a hierarchical porous carbon support.

[0054] Step (4): The hierarchical porous carbon support prepared above is subjected to a secondary carbonization treatment with dihydrodiamine at a mass ratio of 1:25. The HPC is placed at the lower air vent of a tube furnace, and the dihydrodiamine is placed at the upper air vent. Under argon protection, the temperature is increased from room temperature to 800℃ at a rate of 5℃ / min and held for 360 minutes. During this process, the carbon source generated by the decomposition of dihydrodiamine, under the action of a cobalt catalyst, grows carbon nanotubes in situ on the pore surface of the hierarchical porous carbon, resulting in a specific surface area of ​​253.7 m². 2 ·g -1 Porous carbon matrix with pore size ≤160nm.

[0055] Step (5): Carbon nanofibers are used as the current collector for the positive electrode. Sublimed sulfur (S): porous composite material (Co-HPC-CNT-X): polyvinylidene fluoride (PVDF): conductive carbon black (Super P) are added to N-methylpyrrolidone (NMP) solvent at a mass ratio of 60:25:5:10 to prepare the positive electrode slurry. The slurry is evenly dropped onto a carbon paper disc with a diameter of 12 mm and thoroughly dried in an oven at 50 °C to obtain the composite positive electrode.

[0056] Scanning electron microscopy (SEM) was performed on the prepared nitrogen-doped carbon nanotube-supported cobalt metal material. The test results are as follows: Figure 2 As shown. By Figure 2As can be seen, the carbon framework exhibits a typical porous structure, with carbon nanotubes covering the surface and pores of the porous carbon material. Simultaneously, the carbon nanotubes intersect and stack to form new pores. Furthermore, it can be observed that the growth of carbon nanotubes does not destroy the main structure of the porous carbon material, but rather forms a composite structure with it.

[0057] Example 2

[0058] The difference from Example 1 is that in step (4), the mass ratio of the hierarchical porous carbon support to the nitrogen-containing carbon source is 1:5, and a composite cathode is finally obtained.

[0059] Example 3

[0060] The difference from Example 1 is that in step (4), the mass ratio of the hierarchical porous carbon support to the nitrogen-containing carbon source is 1:3, and a composite cathode is finally obtained.

[0061] Example 4

[0062] The difference from Example 1 is that the mass percentage of metal atoms in the composite cathode material is 1%, resulting in a composite cathode.

[0063] Example 5

[0064] The difference from Example 1 is that the mass percentage of metal atoms in the composite cathode material is 0.5%, resulting in a composite cathode.

[0065] Example 6

[0066] The difference from Example 1 is that the specific surface area of ​​the porous carbon matrix in step (2) is 234 m². 2 ·g -1 Ultimately, a composite positive electrode is obtained.

[0067] Example 7

[0068] The difference from Example 1 is that the specific surface area of ​​the porous carbon matrix in step (2) is 143 m². 2 ·g -1 Ultimately, a composite positive electrode is obtained.

[0069] Example 8

[0070] The difference from Example 1 is that in step (4), melamine is replaced with dihydrodiamine, and a composite cathode is finally obtained.

[0071] Comparative Example 1

[0072] The difference from Example 5 is that dihydrodiamine is not added in step (4), and a composite cathode is finally obtained.

[0073] Comparative Example 2

[0074] The difference from Example 5 is that cobalt acetate tetrahydrate is not added in step (1), and a composite cathode is finally obtained.

[0075] Comparative Example 3

[0076] The difference from Example 5 is that in step (4), citric acid is replaced with dihydrodiamine, and a composite cathode is finally obtained.

[0077] Comparative Example 4

[0078] The difference from Example 1 is that step (2) only performs a first-stage carbonization process. The first carbonization process is to raise the temperature from 200°C to 500°C at a rate of 3°C / min and keep it at that temperature for 180 minutes to finally obtain a composite cathode.

[0079] The composite cathode materials prepared in Example 1 and Comparative Example 1 were structurally characterized. Figure 3 The XRD patterns of the two samples are shown in comparison. Figure 3 As can be seen, both samples exhibited typical (002) crystal plane diffraction peaks of carbon materials near 2θ=26°, corresponding to the layered structure of graphitized carbon. The composite cathode material of Example 1 showed sharp (002) crystal plane diffraction peaks, while the composite cathode material of Comparative Example 1 showed broader (002) crystal plane diffraction peaks. This can be attributed to the introduction of highly crystalline carbon nanotubes, which improved the crystallinity of the material. Highly crystalline carbon nanotubes can significantly improve the conductivity of the electrode.

[0080] The composite cathode materials prepared in Example 1 and Comparative Example 1 were structurally characterized. Figure 4 The XPS comparison images of the two samples are shown. Figure 4 As can be seen, both materials have characteristic peaks of C 1s, O 1s and Co 2p, and the composite cathode material of Example 1 has a significant N 1s characteristic peak, indicating that the introduction of dihydrodiamine as a carbon source for growing carbon nanotubes simultaneously achieves nitrogen doping of carbon materials, which is beneficial to enhancing its chemical adsorption capacity for polysulfides.

[0081] Performance testing:

[0082] Specific surface area and pore size of the porous carbon matrix: The pore structure characteristics of the samples were analyzed by measuring the adsorption-desorption isotherm of nitrogen (N2) using a surface area and porosity measurement system (Micromeritics, ASAP 2460). 100 mg of sample was taken and degassed under vacuum at 300 °C for 6 h to remove adsorbed gases, followed by adsorption-desorption tests under a nitrogen atmosphere.

[0083] The composite positive electrodes obtained from the above examples and comparative examples were assembled into CR2025 button batteries in an argon-filled glove box (H2O<0.1 ppm, O2<0.1 ppm) in the following order: positive electrode shell, positive electrode material, electrolyte, separator, negative electrode, gasket, spring, and negative electrode shell. The lithium-sulfur batteries were then tested under room temperature conditions.

[0084] The test results are shown in Table 1.

[0085] Table 1

[0086]

[0087] From the above description, it can be seen that metal sources and nitrogen-containing carbon sources play a decisive role in the in-situ growth of carbon nanotubes. The higher the amount of metal sources and nitrogen-containing carbon sources added, the more favorable it is for the growth of carbon nanotubes. The resulting composite material has a larger average pore size, which can suppress the shuttle effect of polysulfides and thus exhibit a higher capacity retention rate. The porous carbon matrix with a large specific surface area and the doping of nitrogen provide more active sites, enhance the adsorption capacity of polysulfides, and thus exhibit a higher capacity retention rate.

[0088] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0089] The above are merely preferred embodiments of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A composite cathode material, characterized in that, The composite cathode material comprises a porous carbon matrix, metal atoms, and carbon nanotubes. The metal atoms are randomly distributed in the pores and surface of the porous carbon matrix. The carbon nanotubes are grown in situ in the pores and surface of the porous carbon matrix using metal atoms as catalysts, and nitrogen atoms are introduced during the growth process of the carbon nanotubes.

2. The composite cathode material according to claim 1, characterized in that, The mass ratio of the carbon nanotubes to the porous carbon matrix is ​​1~5:19, and the specific surface area of ​​the porous carbon matrix is ​​169~253.7 m². 2 ·g -1 The pore size of the porous carbon matrix is ​​≤160nm.

3. The composite cathode material according to claim 1 or 2, characterized in that, The metal atoms are selected from any one or more of cobalt atoms, iron atoms, and nickel atoms, and the mass percentage of the metal atoms in the composite cathode material is 1% to 5%.

4. A method for preparing the composite cathode material according to any one of claims 1 to 3, characterized in that, The preparation method includes: Step S1: The raw materials, including organic carbon source, soluble salt template and deionized water, are heated and stirred to obtain a mixture. Step S2: The raw materials including the mixture and the metal salt catalyst are stirred and mixed, and then freeze-dried to obtain the precursor dry gel. Step S3: In a first inert atmosphere, the precursor dry gel is subjected to a first carbonization treatment to form a porous carbon skeleton. Step S4: The porous carbon framework is successively ground, washed and dried to obtain a hierarchical porous carbon support; Step S5: In a second inert atmosphere, the raw materials including the hierarchical porous carbon support and the nitrogen-containing carbon source are subjected to a second carbonization treatment to obtain the composite cathode material. The first carbonization process includes a first-stage carbonization process and a second-stage carbonization process performed sequentially, wherein the temperature of the second-stage carbonization process is higher than the temperature of the first-stage carbonization process.

5. The method for preparing the composite cathode material according to claim 4, characterized in that, Step S1 satisfies at least one of the following conditions: (1) The organic carbon source is selected from any one or more of natural high molecular weight starch, cotton, and soybean; (2) The soluble salt template is selected from any one or more of sodium chloride, magnesium chloride, and calcium chloride; (3) The stirring speed is 300~500 rpm; (4) The heating and stirring time is 0.1~0.5h; (5) The heating and stirring temperature is 45~60 ℃.

6. The method for preparing the composite cathode material according to claim 4, characterized in that, Step S2 satisfies at least one of the following conditions: (1) The metal salt catalyst is selected from any one or more of cobalt acetate tetrahydrate, cobalt sulfate, cobalt nitrate, and cobalt chloride; (2) The freeze-drying temperature is -20~35 ℃; (3) The freeze-drying time is 12-16 h; (4) The stirring speed is 500~800 rpm; (5) The mixing time is 0.5~1 h.

7. The method for preparing the composite cathode material according to claim 4, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The first inert atmosphere is selected from any one or more of Ar and N2; (2) The primary carbonization process includes: at 1~3℃·min -1 The heating rate is from room temperature to 200-300℃ and held for 60-120 minutes; the secondary carbonization process includes: heating at 3-5℃·min -1 The heating rate is increased from 200~300℃ to 500~600℃ and held for 60~120 minutes; (3) The drying temperature is 40~50℃ and the drying time is 6~12h.

8. The method for preparing the composite cathode material according to claim 4, characterized in that, Step S5 satisfies at least one of the following conditions: (1) The second carbonization process includes: at 3~5℃·min -1 The heating rate was increased from room temperature to 800℃ and held for 300~360 minutes; (2) The mass ratio of the hierarchical porous carbon support to the nitrogen-containing carbon source is 1:5~25; (3) The nitrogen-containing carbon source is selected from any one or more of dihydrodiamine and melamine; (4) The average particle size of the composite cathode material is 56~124 nm; (5) The first inert atmosphere is selected from any one or more of Ar and N2.

9. A lithium-sulfur battery positive electrode sheet, comprising a positive electrode material, characterized in that, The cathode material is the composite cathode material according to any one of claims 1 to 3 or prepared by any one of claims 4 to 8.

10. A lithium-sulfur battery, comprising a positive electrode and a negative electrode, characterized in that, The positive electrode is the lithium-sulfur battery positive electrode as described in claim 9.

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