A porous carbon material for a lithium-sulfur battery positive electrode and a method of preparing the same

Abstract

The application discloses a kind of porous carbon materials for lithium-sulfur battery positive pole and preparation method thereof, it is related to material preparation technical field, utilize the MOF of different particle size PS template to carry out pore making, and load Ce element and carry out modification, finally high-temperature carbonization synthesis ordered porous morphology MOF derived carbon material, its porous structure can more accommodate lithium-sulfur battery active material sulfur / lithium sulfide, also can make active site more exposure, to improve the utilization of active center.Carbonization can improve its structural stability and conductivity, as active center Ce atom due to its unique characteristics, can be realized by receiving and giving electron catalytic electrochemical reaction electrochemical activity.Cerium element polarity is higher, can provide strong polar adsorption effect, realize adsorption+catalytic conversion combination.Effective improvement active material utilization, inhibit the shuttle effect, improve the electrochemical performance and cycle life of lithium-sulfur battery.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a porous carbon material for lithium-sulfur battery cathodes and its preparation method. Background Technology

[0002] Lithium-sulfur batteries possess advantages such as high theoretical energy density, high theoretical specific capacity, low cost, and environmental friendliness, making them a key focus for researchers as a next-generation energy storage system. While lithium-sulfur batteries offer significant advantages, their inherent drawbacks cannot be ignored, including low cathode conductivity, lithium dendrite growth, and the shuttle effect. These are problems that must be overcome for lithium-sulfur batteries to achieve commercialization.

[0003] Metal-organic frameworks (MOFs) have shown potential application value in lithium-sulfur (Li-S) battery cathode materials due to their unique structural and performance characteristics. MOFs possess advantages such as high specific surface area, tunable pore structure, and ease of functionalization. These characteristics enable MOFs to provide abundant active sites, improve sulfur loading and dispersion, and enhance the kinetics of electrochemical reactions. For example, patent publication number CN109904455B discloses a lithium-sulfur battery cathode support material and its preparation method. The material consists of multilayer porous carbon sheets and CoS2 nanoparticles. The multilayer porous carbon sheets are formed by assembling carbon nanosheet units layer by layer. Within the carbon nanosheet units, porous carbon derived from metal-organic frameworks is densely grown on both sides of reduced graphene oxide. CoS2 nanoparticles are embedded within the porous carbon nanosheets, with a particle size of 5-35 nm. With a large specific surface area and abundant porous structure, MOFs can physically adsorb polysulfides, effectively mitigating their volume expansion and promoting rapid ion and electron transport.

[0004] Based on the above search and combined with existing technology, it was found that existing metal-organic framework (MOF) materials have problems such as small pore size, which makes it difficult to permeate electrolyte and active materials, poor conductivity, and weak adsorption-catalysis ability. These problems hinder the application of MOF-based materials in lithium-sulfur batteries. Therefore, a porous carbon material for lithium-sulfur battery cathode and its preparation method are proposed to improve the above problems. Summary of the Invention

[0005] The purpose of this application is to provide a porous carbon material for the cathode of lithium-sulfur batteries and a method for preparing the same, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, this application provides the following technical solution: a method for preparing porous carbon materials for lithium-sulfur battery cathodes, comprising the following steps:

[0007] S1. Styrene washed with sodium hydroxide and polyvinylpyrrolidone are polymerized into PS under oil bath conditions;

[0008] S2. PS was soaked in methanol solution of cerium nitrate and methanol solution of zinc nitrate + dimethylimidazolium in sequence.

[0009] S3. The treated PS is immersed in a mixed solution of methanol and ammonia to grow MOF.

[0010] S4. After soaking in THF or DMF and centrifuging to remove PS, a white powder is obtained. The white powder is then annealed in a tube furnace to obtain porous MOF-derived carbon SOM-Ce.

[0011] As a further supplement to this scheme, the preparation method of PS includes the following steps:

[0012] S11. Mix 50 mL of styrene with 15 mL of sodium hydroxide in a separatory funnel to remove the polymerization inhibitor and acidic impurities, and then wash with water 3 times to remove the residual sodium hydroxide.

[0013] S12. Add the treated styrene to a 1000mL three-necked flask, add 400mL of distilled water and 1.7g of polyvinylpyrrolidone, stir under an inert atmosphere with bubbling, then keep warm under oil bath heating, then add 60mL of 10% potassium persulfate as an initiator, and polymerize under oil bath heating.

[0014] S13. The white suspension after polymerization is filtered and washed with distilled water, and then the residual moisture is removed in a 40°C forced-air drying oven.

[0015] As a further supplement to this scheme, in S11, the concentration of sodium hydroxide is 5-15%, and the volume ratio of styrene to sodium hydroxide is (1.5-8):1;

[0016] In S12, the mass ratio of polyvinylpyrrolidone to potassium persulfate is (2-4):1.

[0017] As a further supplement to this scheme, in S12, the inert atmosphere bubbling time is 10-30 min, the inert atmosphere is argon or nitrogen, and the heat preservation oil bath time before adding the initiator is 30-60 min to ensure the temperature stability of the system.

[0018] As a further supplement to this scheme, in S12, the heating temperature of the polymerization reaction under oil bath heating is 80-95℃, the reaction time is 22-26h, and the magnetic stirring speed is 200-600r / min.

[0019] As a further supplement to this scheme, in S2, the ratio of zinc nitrate to dimethylimidazole is 1:(1-1.25), the methanol solution is 50-100mL, the concentration of nitrate is 0-32mmol / L, the nitrate includes one or more of cerium nitrate, lanthanum nitrate, indium nitrate, and ferric nitrate, and the concentration of nitrate in methanol is 5-50mg / mL, the soaking time is 2-8h, and the drying temperature after soaking is 40℃, and the time is 8-24h.

[0020] As a further supplement to this scheme, in S3, the ratio of methanol to ammonia is (0-60mL):(0-60mL), and ultrasonication for 3-5 minutes is used to accelerate the nucleation and growth of MOF materials at the beginning of soaking.

[0021] As a further supplement to this scheme, in S4, the amount of THF or DMF used is 200-1000mL, the soaking time is 20-30h, the solvent for subsequent centrifugation is THF or DMF, the number of centrifugations is 5-6, the speed is 5000-6000r / min, each centrifugation is 5-8min, the drying temperature is 110℃, and the drying time is 12-24h.

[0022] As a further supplement to this scheme, in S4, the carbonization temperature of the annealing is 800-1000℃, the heating rate is 1-5℃ / min, the calcination time is 2-4h, and the atmosphere is argon or nitrogen.

[0023] A porous carbon material for the cathode of a lithium-sulfur battery, wherein the porous carbon material is prepared according to the above-described method for preparing a porous carbon material for the cathode of a lithium-sulfur battery.

[0024] In summary, the technical effects and advantages of this invention are as follows:

[0025] 1. This invention synthesizes MOF-derived carbon materials with ordered porous morphology using a template method. Its porous structure can accommodate more sulfur / lithium sulfide, the active material in lithium-sulfur batteries, and also exposes more active sites, thereby improving the utilization rate of the active centers. Due to its unique properties, the Ce atom, as the active center, can freely switch between +3 and +4 valence states, catalyzing electrochemical reactions by accepting and donating electrons. Simultaneously, cerium's polarity is higher than commonly used transition metals (including Ni, Co, Mn, Fe, etc.), providing strong polar adsorption. This achieves a combination of adsorption and catalytic conversion, improving the utilization rate of active materials, suppressing the shuttle effect, and enhancing the electrochemical performance and cycle life of lithium-sulfur batteries.

[0026] 2. The preparation method of this invention is scientific, reasonable, easy to implement, and low in cost. The resulting ordered porous cerium-doped MOF is simple to synthesize and has easily adjustable coordination composition. Li2S / SOM-Ce releases high specific capacities of 765, 715, and 698 mAh / g in the first cycle at 0.1C, respectively. The charge-discharge efficiencies of the first three cycles are 93.5%, 97.6%, and 98.9%, respectively. This effectively improves the utilization rate of active materials, suppresses the shuttle effect, and improves the electrochemical performance and cycle life of lithium-sulfur batteries, providing an important reference for the next generation of high-performance lithium-sulfur batteries based on lithium sulfide. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the 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.

[0028] Figure 1 SEM image and (ef) elemental mapping of the prepared (ab) polystyrene microspheres (PS);

[0029] Figure 2 SEM image of the prepared (ac)cerium-doped MOF grown in a PS template;

[0030] Figure 3 SEM image and (df) elemental mapping of the prepared (ac)SOM-Ce;

[0031] Figure 4 EIS spectrum of Li2S / SOM-Ce;

[0032] Figure 5 for Figure 4 CV plot of Li2S / SOM-Ce;

[0033] Figure 6 The charge-discharge curves of Li2S / SOM-Ce at 0.1C are shown. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example: In this scheme, the preparation method of porous carbon material for lithium-sulfur battery cathode mainly includes the preparation of PS and the preparation of SOM-Ce.

[0036] Example 1:

[0037] I. Preparation of PS:

[0038] (1) Add 50ml of styrene and 15mL of 15% sodium hydroxide solution to a 150mL separatory funnel, shake vigorously to make them fully contact, remove the lower aqueous solution, and keep the upper oil solution to remove the polymerization inhibitor and acidic impurities. Then wash repeatedly with distilled water 3-5 times, 50mL each time, to remove residual sodium hydroxide.

[0039] (2) The cleaned styrene was added to a 1000 mL three-necked flask, along with 400 mL of distilled water and 1.7 g of polyvinylpyrrolidone (PVP) with a particle size of 100-500 nm. The mixture was stirred for 20 min under an inert atmosphere with bubbling, and then kept at 92 °C for 40 min. 60 mL of a 10% potassium persulfate aqueous solution was added as an initiator. The mixture was then stirred at 92 °C for 22-26 h at a speed of 400 r / min. The resulting white suspension was filtered and repeatedly washed with water to form a PS filter cake, which was then dried at 40 °C with forced air.

[0040] It should be further explained that, in the above process, by precisely controlling the polymerization reaction conditions, PS templates with different particle sizes can be obtained, which in turn affects the pore size and distribution of MOF materials.

[0041] II. Preparation of SOM-Ce:

[0042] (1) The PS filter cake was soaked in a 4 mmol / L cerium nitrate methanol solution for 2 hours, and then vacuum dried overnight;

[0043] (2) The PS filter cake was soaked in a methanol solution of zinc nitrate and dimethylimidazole for 6 hours. The amounts of zinc nitrate and dimethylimidazole were 3g and 4g respectively (taking 50mL methanol solution as an example), and then vacuum dried overnight.

[0044] (3) Soak the PS filter cake in a mixed solution of methanol and ammonia, and use strong stirring or sonication for 3-5 minutes to help it grow and nucleate rapidly. Then let it grow at room temperature for 22-26 hours, filter the solution under vacuum, and then vacuum dry it overnight.

[0045] (4) The dried material was stirred in 400 mL of THF solution for 24 h to remove the PS template. Then it was centrifuged at 5000 r / min for 3-5 times, 4-8 min each time. Then it was dried overnight in a forced-air drying oven at 110 °C to completely remove THF. After annealing at 1000 °C, the cerium-doped ordered mesoporous MOF-derived carbon material SOM-Ce was obtained.

[0046] SOM-Ce is compounded with lithium sulfide, then stirred with conductive agents and binders, coated and dried to form uniform electrode sheets, and assembled into lithium-sulfur batteries.

[0047] in, Figure 1 The image shows the SEM image of PS obtained in Example 1. The elements, structure and particle size of PS can be observed from the image. PS is a smooth spherical shape with a particle size of 120-180nm and mainly contains three elements: C, H and O.

[0048] in, Figure 2 This is a SEM image of the ordered porous cerium-doped MOF grown in a PS template in Example 1. Figure 2 As can be seen, ordered porous cerium-doped MOFs grow in bulk PS templates. Due to the combination of Ce and Zn ions on the surface of the PS template during the immersion process, they participate in the assembly process of MOFs. After the PS template is removed, uniformly distributed and uniformly sized pores are formed on the surface of the MOF.

[0049] in, Figure 3 This is a SEM image of the ordered porous cerium-doped MOF-derived carbon material SOM-Ce in Example 1. Figure 3 As can be seen, SOM-Ce has a regular polyhedral shape with uniformly distributed pores of consistent size on the outside, which is beneficial for the loading of active materials and the penetration of electrolyte. High-temperature carbonization helps to improve the electrical conductivity and electrochemical stability of the material. Ultimately, the content of Ce in SOM-Ce is 0.4% (atomic ratio), the content of C is 90.4% (atomic ratio), the content of N is 4.4% (atomic ratio), and the content of O is 4.8% (atomic ratio).

[0050] In addition, through Figure 4 EIS spectra and Figure 5 The CV test results show that the SOM-Ce material has excellent performance in terms of electrical conductivity (charge transfer impedance Rct = 127Ω) and electrochemical activity (CV peak current response reaches 1.3mA). Figure 5The charge-discharge curves show that Li₂S / SOM-Ce releases high specific capacities of 765, 715, and 698 mAh / g in the first cycle at 0.1C, with charge-discharge efficiencies of 93.5%, 97.6%, and 98.9% for the first three cycles, respectively. This indicates that the addition of Ce effectively improves the utilization rate of active materials, suppresses the shuttle effect, and enhances the electrochemical performance and cycle life of lithium-sulfur batteries. These test results provide strong evidence for the practical application of SOM-Ce materials in lithium-sulfur-based lithium-sulfur batteries.

[0051] Example 2:

[0052] I. Preparation of PS:

[0053] (1) Add 65 mL of styrene and 15 mL of 15% sodium hydroxide solution to a 150 mL separatory funnel, shake vigorously to ensure complete contact, remove the lower aqueous layer, and keep the upper oil solution to remove the polymerization inhibitor and acidic impurities. Then wash repeatedly with distilled water 3-5 times, 50 mL each time, to remove residual sodium hydroxide;

[0054] (2) The cleaned styrene was added to a 1000 mL three-necked flask, along with 400 mL of distilled water and 2.5 g of polyvinylpyrrolidone. The mixture was stirred for 20 min under an inert atmosphere with bubbling. After maintaining the temperature at 92 °C for 40 min, 100 mL of a 10% potassium persulfate aqueous solution was added as an initiator. The mixture was then stirred at 75 °C for 22-26 h at a speed of 400 r / min. The resulting white suspension was filtered and repeatedly washed with water to form a PS filter cake, which was then dried at 40 °C with forced air.

[0055] II. Preparation of SOM-Ce:

[0056] (1) The PS filter cake was soaked in a cerium nitrate methanol solution with a concentration of 8 mmol / L for 4 hours, and then vacuum dried overnight;

[0057] (2) The PS filter cake was soaked in a methanol solution of zinc nitrate and dimethylimidazole for 8 hours. The amounts of zinc nitrate and dimethylimidazole were 3g and 4g respectively (taking 50mL methanol solution as an example), and then vacuum dried overnight.

[0058] (3) Immerse the PS filter cake in a mixed solution of methanol and ammonia, and use strong stirring or sonication for 3-5 minutes to assist its rapid growth and nucleation. Then, let it grow statically at room temperature for 22-26 hours. Vacuum filter the solution and then vacuum dry it overnight.

[0059] (4) The dried material was stirred in 400 mL of THF solution for 24 h to remove the PS template. Then it was centrifuged at 5000 r / min for 3-5 times, 4-8 min each time. Then it was dried overnight in a forced-air drying oven at 110 °C to completely remove THF. After annealing at 1000 °C, the cerium-doped ordered mesoporous MOF-derived carbon material SOM-Ce was obtained.

[0060] SOM-Ce is compounded with lithium sulfide, then stirred with a conductive agent and a binder, coated and dried to form uniform electrode sheets, and assembled into lithium-sulfur batteries.

[0061] The PS template prepared according to the method in Example 2 of this experiment has a particle size of approximately 250-300 nm. Correspondingly, the pore size of the cerium-doped ordered mesoporous MOF and SOM-Ce prepared with this larger particle size PS template also increases. Secondly, due to the increased concentration of cerium nitrate during immersion, the Ce content in SOM-Ce also increases accordingly. Ultimately, the Ce content in SOM-Ce is 0.7% (atomic ratio), the C content is 89.9% (atomic ratio), the N content is 4.5% (atomic ratio), and the O content is 4.9% (atomic ratio). Finally, the electrical conductivity of the SOM-Ce material is [material conductivity] (charge transfer impedance Rct = 124 Ω).

[0062] Comparative Example 1

[0063] Compared to Example 1, Comparative Example 1 removed the Ce methanol solution soaking during the preparation process, while the remaining steps were the same. The final synthesized sample, lacking Ce doping and therefore lacking a catalytic center in its structure, had an initial capacity of 634 mAh / g, a 17% decrease compared to Experimental Example 1.

[0064] Comparative Example 2

[0065] Compared to Example 2, Comparative Example 2 did not undergo high-temperature sintering during preparation, while the remaining steps were the same. Due to the lack of sintering, the final synthesized sample showed insufficient bonding between the Ce element and the MOF, and its electrical conductivity (charge transfer impedance Rct = 151 Ω) was significantly higher than that of Experimental Example 1 (Rct = 127 Ω) and Experimental Example 2 (Rct = 124 Ω). The initial capacity was 589 mAh / g, a decrease of 23%.

[0066] This method utilizes PS templates of different particle sizes to create pores in MOFs and modifies them by loading Ce elements. Finally, high-temperature carbonization synthesizes MOF-derived carbon materials with ordered porous morphologies. Their porous structure can accommodate more sulfur / lithium sulfide, the active material in lithium-sulfur batteries, and also exposes more active sites, thereby improving the utilization rate of active centers. Carbonization improves its structural stability and conductivity; EIS spectra show its low impedance (charge transfer impedance Rct = 127 Ω). Due to its unique properties, Ce atoms, as active centers, can catalyze electrochemical reactions through electron acceptance and donation (CV peak current response reaches 1.3 mA). Simultaneously, the high polarity of cerium provides strong polar adsorption, achieving a combination of adsorption and catalytic conversion.

[0067] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a porous carbon material for the cathode of a lithium-sulfur battery, characterized in that, Includes the following steps: S1. Styrene washed with sodium hydroxide and polyvinylpyrrolidone are polymerized into PS under oil bath conditions; S2. PS was soaked successively in a methanol solution of nitrates and a methanol solution of zinc nitrate + dimethylimidazolium; the nitrates included cerium nitrate. S3. The treated PS is immersed in a mixed solution of methanol and ammonia to grow MOF. S4. After soaking in THF or DMF and centrifuging to remove PS, a white powder is obtained. The white powder is then annealed in a tube furnace to obtain porous MOF-derived carbon SOM-Ce.

2. The method for preparing a porous carbon material for a lithium-sulfur battery cathode according to claim 1, characterized in that: The method for preparing the PS includes the following steps: S11. Mix 50 mL of styrene with 15 mL of sodium hydroxide in a separatory funnel to remove the polymerization inhibitor and acidic impurities, and then wash with water 3 times to remove the residual sodium hydroxide. S12. Add the treated styrene to a 1000 mL three-necked flask, add 400 mL of distilled water and 1.7 g of polyvinylpyrrolidone, stir under an inert atmosphere with bubbling, then keep warm under oil bath heating, then add 60 mL of 10% potassium persulfate as an initiator, and polymerize under oil bath heating. S13. The white suspension after polymerization is filtered and washed with distilled water, and then the residual moisture is removed in a 40 ℃ forced-air drying oven.

3. The method for preparing a porous carbon material for a lithium-sulfur battery cathode according to claim 2, characterized in that: In S11, the concentration of sodium hydroxide is 5-15%, and the volume ratio of styrene to sodium hydroxide is (1.5-8):1; In S12, the mass ratio of polyvinylpyrrolidone to potassium persulfate is (2-4):

1.

4. The method for preparing a porous carbon material for a lithium-sulfur battery cathode according to claim 2, characterized in that: In S12, the inert atmosphere is bubbled for 10-30 minutes, and the inert atmosphere is argon or nitrogen. The insulated oil bath time before adding the initiator is 30-60 minutes to ensure the temperature stability of the system.

5. The method for preparing a porous carbon material for a lithium-sulfur battery cathode according to claim 2, characterized in that: In S12, the heating temperature of the polymerization reaction under oil bath heating is 80-95 ℃, the reaction time is 22-26 h, and the magnetic stirring speed is 200-600 r / min.

6. The method for preparing a porous carbon material for a lithium-sulfur battery cathode according to claim 1, characterized in that: In S2, the ratio of zinc nitrate to dimethylimidazole is 1:(1-1.25), the methanol solution is 50-100 mL, the nitrate concentration is 0-32 mmol / L, and the nitrate also includes one or more of lanthanum nitrate, indium nitrate, and ferric nitrate, and the nitrate concentration in methanol is 5-50 mg / mL, the soaking time is 2-8 h, and the drying temperature after soaking is 40 ℃, and the time is 8-24 h.

7. The method for preparing a porous carbon material for a lithium-sulfur battery cathode according to claim 1, characterized in that: In S3, the ratio of methanol to ammonia is (0-60 mL): (0-60 mL), and ultrasonication is used for 3-5 minutes to accelerate the nucleation and growth of MOF materials at the beginning of soaking.

8. The method for preparing a porous carbon material for a lithium-sulfur battery cathode according to claim 1, characterized in that: In step S4, the amount of THF or DMF used is 200-1000 mL, the soaking time is 20-30 h, the solvent for subsequent centrifugation is THF or DMF, the number of centrifugations is 5-6, the speed is 5000-6000 r / min, each centrifugation is 5-8 min, the drying temperature is 110 ℃, and the drying time is 12-24 h.

9. A method for preparing a porous carbon material for a lithium-sulfur battery cathode according to claim 1, characterized in that: In S4, the carbonization temperature of the annealing is 800-1000 ℃, the heating rate is 1-5 ℃ / min, the calcination time is 2-4 h, and the atmosphere is argon or nitrogen.

10. A porous carbon material for the cathode of a lithium-sulfur battery, characterized in that: The porous carbon material is prepared according to the method for preparing porous carbon material for lithium-sulfur battery cathode as described in any one of claims 1-9.

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