A positive electrode material, a preparation method thereof and a lithium-sulfur battery

Abstract

This application discloses a cathode material and its preparation method, as well as a lithium-sulfur battery. The cathode material includes porous carbon, at least a portion of which is filled with a sulfur-containing polymer. As the cathode material for a lithium-sulfur battery, sulfur is present in the sulfur-containing polymer, and the sulfur chains are fixed by sulfur-carbon chemical bonds, which can inhibit the dissolution and diffusion of lithium polysulfides at the molecular level and avoid the shuttle effect. The porous carbon, on the one hand, constructs a conductive network to improve the overall conductivity of the cathode material, and on the other hand, provides a pore structure for the sulfur-containing polymer, so that the sulfur-containing polymer is encapsulated in the carbon pores. This not only further blocks the diffusion of lithium polysulfides by utilizing the spatial confinement effect of the porous carbon material, but also improves the uniformity of the dispersion of carbon material and sulfur-containing polymer in the cathode material, thereby improving the overall chemical stability of the cathode material and thus improving the cycle performance and rate performance of the lithium-sulfur battery.

Description

Technical Field

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

[0002] Lithium-sulfur batteries, due to the high specific capacity (1675 mAh / g) and high energy density (2600 Wh / kg) of sulfur as the active material, are widely recognized as the core development direction of next-generation high-energy-density battery systems, possessing irreplaceable application potential in electric vehicles, large-scale energy storage power stations, and other fields. However, the commercialization of lithium-sulfur batteries has long been limited by the "shuttle effect" of the cathode material, namely, during charge and discharge, sulfur is converted into soluble lithium polysulfides (Li2S). x (4≤x≤8), these lithium polysulfides diffuse through the electrolyte to the surface of the lithium anode and undergo side reactions, resulting in loss of active material, rapid decay of battery capacity, and decrease in coulombic efficiency.

[0003] Therefore, developing a cathode material suitable for lithium-sulfur batteries that can suppress the shuttle effect in the cathode material and improve the cycle performance and rate performance of lithium-sulfur batteries is a problem that needs to be solved. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode material and preparation method, and a lithium-sulfur battery, aiming to solve the problem that the shuttle effect of the negative electrode of lithium-sulfur batteries leads to unsatisfactory cycle performance and rate performance of lithium-sulfur batteries.

[0005] The first embodiment of this application provides a positive electrode material, comprising porous carbon, wherein at least a portion of the porous carbon is filled with a sulfur-containing polymer; The structural formula of the sulfur-containing polymer is shown in any one of formulas I-1 to I-3:

[0006] Formula I-1;

[0007] Formula I-2;

[0008] Formula I-3; In the formula, n=20~50, m=20~50, p=20~50, q=20~50, a=20~50, b=20~50, c=20~50, d=20~50.

[0009] In some embodiments, the mass ratio of the porous carbon to the sulfur-containing polymer is 20-30:70-80.

[0010] In some embodiments, the porosity of the porous carbon is 0.4~1.2 g / cm³. 3 .

[0011] The second embodiment of this application provides a method for preparing a cathode material, used to prepare the cathode material in any of the above embodiments, comprising the following steps: Porous carbon and a sulfur source are provided, and the sulfur source is heated for the first time to bring it into a molten state. A monomer containing unsaturated bonds is added, and a second heating is performed to allow the monomer and the sulfur source to polymerize in the pores of the porous carbon, yielding an intermediate product. The intermediate product is cooled to obtain the cathode material.

[0012] In some embodiments, the molar ratio of the porous carbon to the sulfur source is 1:3 to 1:6.

[0013] In some embodiments, the mass of the monomer is 5 to 15 wt% of the mass of the sulfur source.

[0014] In some embodiments, the porous carbon includes at least one of ordered mesoporous carbon, carbon nanotubes, activated carbon, and graphene aerogel.

[0015] In some embodiments, the sulfur source comprises elemental sulfur with a purity of 99.9-100%.

[0016] In some embodiments, the monomer includes at least one of tetra(allyloxy)-1,4-benzoquinone, 1,4-diisopropenylbenzene, and trithiocyanuric acid.

[0017] In some embodiments, the temperature of the first heating is 160~170°C.

[0018] In some embodiments, the first heating time is 4 to 6 minutes.

[0019] In some embodiments, the temperature of the second heating is 175~185°C.

[0020] In some embodiments, the polymerization reaction takes 7 to 9 minutes.

[0021] In some embodiments, the cooling time is 5 to 15 minutes, and the final temperature of the cooling is room temperature.

[0022] The third embodiment of this application provides a lithium-sulfur battery, including a positive electrode sheet, wherein the positive electrode sheet includes the positive electrode material in any of the above embodiments, or includes the positive electrode material prepared by the preparation method in any of the above embodiments; The lithium-sulfur battery retains 60% to 70% of its capacity after 500 cycles at 1C current, and its discharge capacity at 3C current is 70% to 80% of the capacity of the first cycle.

[0023] This application provides a cathode material comprising porous carbon, at least a portion of which is filled with a sulfur-containing polymer. As a cathode material for lithium-sulfur batteries, sulfur is present in the sulfur-containing polymer, and the sulfur chains are fixed by sulfur-carbon chemical bonds, which can inhibit the dissolution and diffusion of lithium polysulfides at the molecular level, avoiding the shuttle effect. The porous carbon, on the one hand, constructs a conductive network, improving the overall conductivity of the cathode material; on the other hand, it provides a porous structure for the sulfur-containing polymer, encapsulating the polymer within the carbon pores. This not only further blocks the diffusion of lithium polysulfides through the spatial confinement effect of the porous carbon material, but also improves the uniformity of the dispersion of carbon materials and sulfur-containing polymers in the cathode material, thereby improving the overall chemical stability of the cathode material and ultimately enhancing the cycle performance and rate performance of the lithium-sulfur battery. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a spot scan characterization image of the cathode material provided in Embodiment 1 of this application. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] In the description of this application, it should be noted that "multiple" means two or more, unless otherwise explicitly specified. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include one or more features.

[0028] The compounds of this application can be synthesized via synthetic routes including methods similar to those known in the field of chemistry, particularly with reference to the description contained herein. Starting materials are generally available from commercial sources or can be readily prepared using methods known to those skilled in the art. For illustrative purposes, the reaction schemes described below illustrate possible routes for synthesizing the compounds of this application and key intermediates. For a more detailed description of each reaction step, see the Examples section below. Those skilled in the art will recognize that other suitable starting materials, reagents, and synthetic routes can be used to synthesize the compounds of this application and their various derivatives.

[0029] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure of this application, the configuration and arrangement of specific examples are described below. Of course, these are merely examples and are not intended to limit this application.

[0030] During the charge-discharge cycle of lithium-sulfur batteries, sulfur, the active material at the positive electrode, gradually transforms into a series of soluble lithium polysulfides. These lithium polysulfides are not stably bound by the positive electrode material but diffuse through the electrolyte to the surface of the lithium metal negative electrode. After undergoing irreversible side reactions, they cannot effectively return to the positive electrode, a phenomenon known as the "shuttle effect." To suppress the shuttle effect, one approach is through physical confinement, utilizing the pore structure of porous carbon materials to encapsulate sulfur within the carbon pores. The spatial confinement of the carbon material blocks the diffusion of lithium polysulfides. The core of this approach is the physical combination of sulfur and porous carbon materials, but its ability to confine lithium polysulfides is limited. After long-term cycling, the volume expansion of sulfur will still cause pore rupture, exacerbating the shuttle effect. Another approach is chemical confinement, through reverse sulfurization polymerization, reacting elemental sulfur with organic monomers to generate sulfur-rich polymers. These polymers fix the sulfur chains through sulfur-carbon chemical bonds, which can inhibit the dissolution and diffusion of lithium polysulfides at the molecular level. However, sulfur-rich polymers themselves have extremely poor conductivity and cannot be used as a positive electrode material alone. The existing process for composite sulfur-rich polymers with conductive carbon materials involves mixing elemental sulfur with organic monomers at high temperatures to generate sulfur-rich polymer powder. This powder is then combined with mechanical mixing (such as ball milling or stirring) or heat treatment (heating at 150-180°C for 60-240 minutes to reduce the viscosity of the sulfur-rich polymer, allowing it to spontaneously penetrate into the porous carbon channels). However, mechanical mixing only achieves surface adhesion and cannot truly bond the sulfur-rich polymer with the conductive carbon material. Heat treatment causes the sulfur-carbon chemical bonds in the sulfur-rich polymer molecular chain to break again, degrading the originally regular cross-linked network into short-chain polymers. This results in a loss of chemical binding capacity for lithium polysulfides, leading to decreased chemical stability of the composite material, accelerated dissolution of lithium polysulfides during cycling, and faster battery capacity decay. Furthermore, because the sulfur-rich polymer has formed solid particles, even with viscosity reduction through heating, it is difficult to fully penetrate the micropores of the porous carbon, further exacerbating uneven dispersion and resulting in underutilization of the carbon material's pore space.

[0031] The applicant discovered through research that by designing an in-situ reaction between sulfur powder and monomers within the pores of porous carbon, using the pores of porous carbon as a "reactor," the problem of insufficient utilization of the pore space in conductive carbon materials and the unsatisfactory battery performance caused by polymer agglomeration can be effectively solved.

[0032] The first embodiment of this application provides a positive electrode material, including porous carbon, wherein at least a portion of the porous carbon is filled with a sulfur-containing polymer; The structural formulas of sulfur-containing polymers are shown in any one of formulas I-1 to I-3:

[0033] Formula I-1;

[0034] Formula I-2;

[0035] Formula I-3; In the formula, n=20~50, m=20~50, p=20~50, q=20~50, a=20~50, b=20~50, c=20~50, d=20~50.

[0036] As we can understand it, porous carbon refers to carbon materials with a porous structure, which includes micropores, mesopores, and macropores. Micropores are those with a diameter less than 2 nm, mesopores are those with a diameter between 2 and 50 nm, and macropores are those with a diameter greater than 50 nm. Micropores, mesopores, and macropores can form channels, and these channels can form interconnected networks, which is beneficial for mass transport. As the cathode material for lithium-sulfur batteries, sulfur exists in sulfur-containing polymers. By fixing the sulfur chains through sulfur-carbon chemical bonds, the dissolution and diffusion of lithium polysulfides can be inhibited at the molecular level, avoiding the shuttle effect. Porous carbon, on the one hand, constructs a conductive network to improve the overall conductivity of the cathode material, and on the other hand, provides a pore structure for the sulfur-containing polymers, allowing the sulfur-containing polymers to be encapsulated within the carbon pores. This not only further blocks the diffusion of lithium polysulfides through the spatial confinement effect of porous carbon materials, but also improves the uniformity of the dispersion of carbon materials and sulfur-containing polymers in the cathode material, thereby improving the overall chemical stability of the cathode material and thus improving the cycle performance and rate performance of lithium-sulfur batteries.

[0037] In some embodiments, the mass ratio of porous carbon to sulfur-containing polymer is 20-30:70-80.

[0038] It is understandable that the mass ratio of porous carbon to sulfur-containing polymer can be any value from 20:80, 22:78, 24:76, 26:74, 28:72, 30:70, or any value within a range of any two values. When the mass ratio of porous carbon to sulfur-containing polymer meets the above range, it ensures that the sulfur-containing polymer is fully dispersed in the pore structure of the porous carbon, while balancing the conductivity of the cathode material and avoiding the dissolution and diffusion of lithium polysulfides, thereby improving the overall chemical stability of the cathode material and thus improving the cycle performance and rate performance of lithium-sulfur batteries.

[0039] In some embodiments, the porosity of the porous carbon is 0.4~1.2 g / cm³. 3 .

[0040] It is understandable that the porosity of porous carbon can be as low as 0.4 g / cm³. 3 0.6g / cm 3 0.8g / cm 3 1.0g / cm 3 1.2g / cm 3 The porosity of porous carbon, within any value or any two values ​​in the range, helps provide reaction space for the in-situ polymerization of sulfur and monomers. However, excessive porosity may reduce the conductivity of the carbon material itself. When the porosity of porous carbon meets the above-mentioned value range, it allows sulfur-containing polymers to penetrate into the pores of porous carbon while ensuring the overall conductivity of the cathode material.

[0041] The second embodiment of this application provides a method for preparing a cathode material, used to prepare the cathode material in any of the above embodiments, comprising the following steps: Porous carbon and a sulfur source are provided for the first heating, so that the sulfur source is in a molten state; Add a monomer containing unsaturated bonds, and heat it a second time to allow the monomer and sulfur source to polymerize in the pores of porous carbon, thus obtaining an intermediate product. The intermediate product is cooled to obtain the cathode material.

[0042] Understandably, the preparation method provided in this application uses porous carbon as a "microreactor" to integrate the traditional two-step "sulfur-rich polymer synthesis" and "carbon material composite" into one step. By using gradient temperature control of melt diffusion at 160~170℃ (4~6 min) and in-situ polymerization at 160~170℃ (7~9 min), it eliminates the several hours of time required for pre-synthesis of sulfur-rich polymers and the subsequent 30-60 min steps of high-temperature composite in the traditional process, directly shortening the total process to within 15 min and solving the problems of "cumbersome process flow, time-consuming and energy-intensive". Furthermore, since the polymerization reaction is completed in-situ within the carbon channels, no subsequent heating and penetration are required, avoiding the damage of high temperature to the cross-linked structure of sulfur-rich polymers, ensuring its chemical binding ability to lithium polysulfides, and achieving the invention objective of "protecting the integrity of polymer structure".

[0043] On the other hand, after sulfur melts and is added to liquid monomers, it can help sulfur fully penetrate into the micropores and mesopores of carbon materials. The sulfur-rich polymer generated by subsequent in-situ polymerization can uniformly fill the pores and form a tight interface with the carbon wall. This not only solves the defects of polymer agglomeration and uneven dispersion in traditional mechanical mixing, but also constructs a continuous carbon conductive network and improves rate performance. Furthermore, through the dual effect of "physical confinement of carbon pores + chemical binding of polymers", it effectively suppresses lithium polysulfide shuttle, improving the capacity retention rate of 500 cycles at 1C by about 10%. At the same time, the integrated structure can buffer the volume expansion of sulfur, further enhancing cycle stability and fully responding to the core requirement of "improving electrochemical performance".

[0044] In some embodiments, the molar ratio of porous carbon to sulfur source is 1:3 to 1:6.

[0045] Understandably, the mass ratio of porous carbon to sulfur source can be any value from 1:3, 1:4, 1:5, 1:6 or any value between any two values. This ratio ensures that sulfur can fully fill the carbon channels while avoiding excessive sulfur agglomeration on the carbon surface.

[0046] In some embodiments, the mass of the monomer is 5 to 15 wt% of the mass of the sulfur source.

[0047] It is understandable that the percentage of monomer mass to sulfur source mass can be any value from 5wt%, 7wt%, 9wt%, 11wt%, 13wt%, 15wt%, or any value between any two. Too low a dosage will lead to incomplete polymerization, while too high a dosage will form too many carbon chains, reduce the sulfur content of the material, and affect the specific capacity of the cathode material.

[0048] In some embodiments, porous carbon includes at least one of ordered mesoporous carbon (CMK-3), carbon nanotubes, activated carbon, and graphene aerogel.

[0049] In some embodiments, the sulfur source includes elemental sulfur with a purity of 99.9-100%.

[0050] Specifically, elemental sulfur can be sulfur powder with a particle size of 50~100μm.

[0051] It is understandable that the particle size of sulfur powder can be any value or any two values ​​within the range of 50μm, 60μm, 70μm, 80μm, 90μm, and 100μm. By controlling the particle size of sulfur powder to meet the above range, sulfur powder can be rapidly and uniformly melted during the first heating at 160~170℃. With its good fluidity, it can fully penetrate into the micropores and mesopores of porous carbon, providing a uniform sulfur source for subsequent in-situ polymerization with monomers, avoiding sulfur agglomeration on the carbon surface, ensuring uniform generation of sulfur-containing polymers in the carbon channels, and thus improving the conductivity and chemical stability of the cathode material.

[0052] In some embodiments, a sealed glass bottle with a lid can be used as a reaction vessel. Porous carbon and sulfur powder are placed in the sealed glass reaction vessel and heated, which can prevent sulfur vapor leakage and air entry during the reaction process and avoid sulfur oxidation.

[0053] In some embodiments, the monomer includes at least one of tetra(allyloxy)-1,4-benzoquinone, 1,4-diisopropenylbenzene, and trithiocyanuric acid.

[0054] It is understandable that since the added monomers are also in a molten state at high temperatures, their addition is beneficial for the further uniform dispersion of sulfur, monomers, and carbon.

[0055] In some embodiments, the temperature of the first heating is 160~170°C.

[0056] It is understandable that the initial heating temperature can be any value from 160℃, 162℃, 164℃, 166℃, 168℃, and 170℃, or any value within a range of two. When the initial heating temperature meets the above range, it ensures that the sulfur powder is completely melted and has good fluidity. This allows for uniform distribution of sulfur within the carbon channels through melt diffusion, providing a sulfur source for subsequent in-situ polymerization.

[0057] In some embodiments, the initial heating time is 4 to 6 minutes.

[0058] Understandably, the initial heating time can be any value from 4 min, 4.5 min, 5 min, 5.5 min, and 6 min, or any value within a range of two such values. By controlling the initial heating time to meet the above range, it is possible to ensure that the sulfur source is fully melted and uniformly diffused into the porous carbon channels at 160~170℃, providing a uniform sulfur source for subsequent in-situ polymerization with monomers. At the same time, it avoids insufficient sulfur melting and uneven diffusion due to excessively short heating time, or sulfur vapor loss and increased energy consumption due to excessively long heating time.

[0059] In some embodiments, the temperature of the second heating is 175~185°C.

[0060] Understandably, the temperature for the second heating can be any value from 175℃, 177℃, 179℃, 181℃, 183℃, and 185℃, or any value within a range of two such values. Within this temperature range, the unsaturated bonds of the monomer break, undergoing an addition reaction with the sulfur SS chain to form a cross-linked sulfur-rich polymer with "-SCCS-" as repeating units. This polymer is formed directly within the carbon channels and forms a tight bond with the carbon material surface. When the temperature for the second heating meets the above-mentioned range, the reverse sulfurization polymerization reaction is kept within the optimal reaction temperature range, avoiding extremely slow reaction rates (requiring several hours) due to excessively low temperatures, or excessively high temperatures where the monomers easily undergo self-polymerization, failing to form a sulfur-rich polymer with sulfur. In some embodiments, the polymerization reaction takes 7 to 9 minutes.

[0061] It is understandable that the polymerization reaction time can be any value from 7 min, 7.5 min, 8 min, 8.5 min, and 9 min, or any value within a range of two such values. By controlling the polymerization reaction time to meet the above range, it is possible to ensure that the monomer and molten sulfur undergo sufficient reverse sulfurization polymerization within the porous carbon channels, forming a well-structured cross-linked sulfur-rich polymer. The sulfur chains are stabilized and fixed through sulfur-carbon chemical bonds. At the same time, it avoids incomplete polymerization due to excessively short reaction time, or excessive cross-linking of polymer molecular chains and pore blockage due to excessively long reaction time. This ensures the chemical stability and conductivity of the cathode material, thereby improving the cycle performance and rate performance of lithium-sulfur batteries.

[0062] In some embodiments, the cooling time is 5 to 15 minutes, and the final cooling temperature is room temperature.

[0063] Understandably, the cooling time can be any value from 5 min, 7 min, 9 min, 11 min, 13 min, and 15 min, or any value within a range of two. Rapid cooling avoids the increase in polymer crystallinity caused by slow cooling, which in turn reduces the material's conductivity. By controlling the cooling time to meet the above-mentioned range, it is possible to avoid stress cracks caused by excessively rapid cooling, and also to prevent excessively slow cooling from increasing polymer crystallinity and decreasing conductivity. At the same time, it ensures that the sulfur-containing polymer is stably formed within the porous carbon channels and forms a tight bond with the carbon walls, further improving the structural stability and electrochemical performance of the cathode material.

[0064] The third embodiment of this application provides a lithium-sulfur battery, including a positive electrode sheet, which includes the positive electrode material in any of the above embodiments, or the positive electrode material prepared by the preparation method in any of the above embodiments.

[0065] The cycle performance of the lithium-sulfur battery is 60%~70% after 500 cycles at 1C current, and the rate performance is 70%~80% of the first cycle capacity at 3C current.

[0066] The following description, in conjunction with specific embodiments, illustrates a solid electrolyte separator, its preparation method, and a lithium battery provided in this application: Example 1 S1. Mix CMK-3 and sulfur powder at a molar ratio of 1:5 and place in a sealed glass container. The porosity of CMK-3 is 0.8 g / cm³. 3 The sulfur powder has a purity of ≥99.9% and a particle size of 50μm. S2. Perform the first heating, control the temperature at 165℃, and hold for 5 minutes to allow sulfur to diffuse into the channels of CMK-3 through melting. S3. Add tetra(allyloxy)-1,4-benzoquinone monomer, the mass of which is 10 wt% of the mass of sulfur. Increase the temperature from 165°C to 180°C and start stirring to allow the tetra(allyloxy)-1,4-benzoquinone monomer and sulfur source to polymerize in the pores of porous carbon. The reaction takes about 8 minutes. The reaction ends when the viscosity of the entire composite system rises to the point where stirring can no longer proceed and is stopped. Continue stirring for about 2 minutes to obtain the intermediate product. S4. The glass container is rapidly cooled using an ice-water bath to room temperature within 5 minutes, resulting in a black powdery cathode material.

[0067] The cathode material prepared in Example 1 was observed using a scanning electron microscope, and the characterization diagram is shown below. Figure 1 As shown, the sulfur-containing polymer is uniformly filled in the pores of the carbon material without obvious agglomeration.

[0068] The conductivity of the positive electrode material prepared in Example 1 was tested, and its conductivity was 2.16 × 10⁻⁶. -2 S / cm.

[0069] Examples 2-6 The preparation methods provided in Examples 2-6 are the same as those in Example 1, with the only difference being the adjustment of process parameters.

[0070] Comparative Examples 1-4 The preparation methods provided in Comparative Examples 1-4 are the same as those in Example 1, with the only difference being the adjustment of process parameters.

[0071] The parameters in Examples 1-6 and Comparative Examples 1-4 are shown in Table 1.

[0072] Table 1 Porous carbon: sulfur (molar ratio) Monomer: Sulfur wt% First temperature rise ℃ reaction time min Second temperature rise ℃ reaction time min Cooldown time Example 1 0.2:1 70% 165 5 180 8 Quick ice bath Example 2 0.2:1 70% 165 5 180 8 Quick ice bath Example 3 0.1:1 70% 165 5 180 8 Quick ice bath Example 4 0.2:1 75% 165 5 180 8 Quick ice bath Example 5 0.1:1 75% 165 5 180 8 Let stand at room temperature Example 6 0.2:1 75% 155 5 180 3 Quick ice bath Comparative Example 1 0.2:1 75% 155 10 180 3 Quick ice bath Comparative Example 2 0.2:1 75% 155 15 180 3 Quick ice bath Comparative Example 3 0.2:1 75% 155 5 190 3 Quick ice bath Comparative Example 4 0.2:1 75% 155 5 200 3 Quick ice bath The cathode materials obtained from the above embodiments and comparative examples were used to prepare lithium-sulfur batteries, and their electrical performance was tested. The results are shown in Table 2.

[0073] Table 2 Cyclic performance Ratio performance Example 1 78.6% 72.3% Example 2 79% 73.3% Example 3 80.2% 77.2% Example 4 79.5% 75.3% Example 5 82.0% 75.7% Example 6 81.9% 78% Comparative Example 1 67.2% 71.1% Comparative Example 2 62.9% 67.6% Comparative Example 3 71.2% 70.4% Comparative Example 4 72.1% 70.2% As shown in Tables 1 and 2, the cathode material provided in this application exhibits relatively ideal cycle performance and rate performance. Comparative Examples 1, 2, and 6 show that an excessively long initial heating time leads to a decrease in the cycle performance of the lithium-sulfur battery. Comparative Examples 3 and 4 show that an excessively high second heating temperature causes monomer self-polymerization, resulting in a subsequent decrease in the cycle performance and rate performance of the lithium-sulfur battery.

[0074] The foregoing has provided a detailed description of a cathode material and its preparation method, as well as a lithium-sulfur battery, according to the embodiments of this application. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A positive electrode material, characterized in that, It includes porous carbon, at least a portion of which is filled with a sulfur-containing polymer; The structural formula of the sulfur-containing polymer is shown in any one of formulas I-1 to I-3: Formula I-1; Formula I-2; Formula I-3; In the formula, n=20~50, m=20~50, p=20~50, q=20~50, a=20~50, b=20~50, c=20~50, d=20~50.

2. The cathode material according to claim 1, characterized in that, The mass ratio of the porous carbon to the sulfur-containing polymer is 20~30:70~80.

3. The cathode material according to claim 1, characterized in that, The porous carbon has a porosity of 0.4~1.2 g / cm³. 3 .

4. A method for preparing a cathode material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Porous carbon and a sulfur source are provided, and the sulfur source is heated for the first time to bring it into a molten state. A monomer containing unsaturated bonds is added, and a second heating is performed to allow the monomer and the sulfur source to polymerize in the pores of the porous carbon, yielding an intermediate product. The intermediate product is cooled to obtain the cathode material.

5. The method for preparing the cathode material according to claim 4, characterized in that, The molar ratio of the porous carbon to the sulfur source is 1:3 to 1:6; and / or, The mass of the monomer is 5 to 15 wt% of the mass of the sulfur source.

6. The method for preparing the cathode material according to claim 4, characterized in that, The porous carbon includes at least one of ordered mesoporous carbon, carbon nanotubes, activated carbon, and graphene aerogel; and / or, The sulfur source includes elemental sulfur, the purity of which is 99.9% to 100%; and / or, The monomer includes at least one of tetra(allyloxy)-1,4-benzoquinone, 1,4-diisopropenylbenzene, and trithiocyanuric acid.

7. The method for preparing the cathode material according to claim 4, characterized in that, The temperature of the first heating is 160~170℃; and / or, The first heating time is 4-6 minutes.

8. The method for preparing the cathode material according to claim 4, characterized in that, The temperature of the second heating is 160~170℃; and / or, The polymerization reaction takes 7 to 9 minutes.

9. The method for preparing the cathode material according to claim 4, characterized in that, The cooling time is 5 to 15 minutes, and the final temperature of the cooling is room temperature.

10. A lithium-sulfur battery, characterized in that, Includes a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material as described in any one of claims 1 to 3, or comprises the positive electrode material prepared by the preparation method as described in any one of claims 4 to 9; The lithium-sulfur battery retains 60% to 70% of its capacity after 500 cycles at 1C current, and its discharge capacity at 3C current is 70% to 80% of the capacity of the first cycle.

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