CN113649043B - Preparation method of a highly loaded Mn-N active site doped carbon material catalyst and its application in lithium-sulfur batteries - Google Patents

Abstract

The invention provides a preparation method of a highly loaded Mn-N active site doped carbon material catalyst and its application in a lithium-sulfur battery, belonging to the field of energy storage batteries. The catalyst uses manganese-doped zinc-based metal-organic framework Mn‑ZIF‑8 as a precursor. After high-temperature pyrolysis evaporation of zinc and Zn atoms and ammonia gas _NH3 treatment to increase the number of vacancies and nitrogen atomic anchor sites on the substrate material, and then secondary Adsorption of manganese ions increases the doping amount of Mn-N sites. In the two steps of the synthesis method, in-situ loading of Mn-N sites is adopted, and the pore structure of the catalyst is optimized and the doping amount of nitrogen atoms is increased. When the catalyst prepared by the invention is applied to a lithium-sulfur battery, the highly loaded Mn-N active sites and nitrogen atoms not only increase the catalyst's catalysis and adsorption effects on polysulfides, but also the high-conductivity carbon material substrate ensures that the sulfur element is And the higher utilization rate of Li ₂ S/Li ₂ S ₂ .

Description

A kind of preparation method of highly loaded Mn-N active site doped carbon material catalyst and the same Application in Lithium Sulfur Batteries

technical field

The invention belongs to the field of electrochemistry, and relates to a Mn-N active site doped carbon material catalyst and a preparation method and application thereof, in particular to a preparation method of a highly loaded Mn-N active site doped carbon material catalyst and the same As a modification material, it is used as a modification material for lithium-sulfur battery separators to achieve catalytic and adsorption effects on polysulfides.

Background technique

Lithium-sulfur battery is a new type of secondary energy storage battery with high theoretical specific capacity (1675mAh g ^-1 ) and energy density (2600Wh kg ^-1 ). Low cost, low pollution and other advantages. Therefore, it is a promising secondary energy storage system. However, its many shortcomings greatly limit its development: (1) the insulating properties of sulfur lead to its low utilization rate (conductivity is about 5×10 ^-30 S cm ^-1 , 25℃); (2) ) The volume change inside the battery during charging and discharging is large (about 80%); (3) The specific capacity declines faster and the coulombic efficiency is lower due to the "shuttle effect" of polysulfides.

In response to the above problems, researchers have proposed many solutions. The results show that the introduction of highly conductive materials (carbon materials, MXene) and sulfur can effectively improve the utilization of sulfur. By adopting a high specific surface area (hollow structure, core-shell structure), the volume change during the charging and discharging process can be effectively alleviated, and the safety of the battery can be ensured. The "shuttle effect" is inhibited by two physical/chemical effects. One is to use "molecular sieve" to prevent the diffusion of polysulfides to the negative electrode region; the other is to form chemical bonds with polysulfides to limit its diffusion.

When metal-nitrogen (M-N) active sites are supported on carbon materials as catalysts for lithium-sulfur batteries, the excellent catalysis and anchoring effect of M-N active sites can accelerate the conversion of polysulfides and limit their diffusion; at the same time, The excellent electrical conductivity of carbon-based materials can also effectively improve the utilization of sulfur and discharge products. However, the low loading of M-N active sites on carbon materials has always been the biggest problem faced by this type of catalysts. Especially for the preparation of highly loaded manganese-nitrogen (Mn-N) active site doped carbon catalysts, because manganese has more valence states (0-+7), it is easy to form compounds; at the same time, it is very easy to agglomerate during the pyrolysis process Clustering or particle structure etc. make the preparation of the catalyst more difficult.

In order to solve the above problems, the present invention adopts a two-step in-situ preparation of highly loaded Mn-N active sites, which has the following advantages: (1) the used process can effectively improve the Mn-N active sites in the Loading amount on carbon materials; (2) Metal organic framework (MOF) intrinsically high nitrogen content and ammonia treatment can greatly increase the doping amount of nitrogen atoms; (3) Ammonia etching effect and zinc atom evaporation The pore structure of the catalyst can be greatly optimized; (4) the preparation steps of the entire experimental process are in-situ doping of active sites, which is beneficial to further optimization of the catalyst performance.

SUMMARY OF THE INVENTION

In view of the deficiencies of the synthesis methods in the prior art, the present invention provides a preparation method for in-situ preparation of a highly loaded Mn-N active site doped carbon material catalyst and its application in a lithium-sulfur battery. For the preparation of this catalyst, the “doping” step was first used to introduce Mn ²⁺ (manganese acetate) to form a Mn-ZIF-8 precursor in ZIF-8 as the first step to in situ prepare the Mn-N active site supported catalyst. After two-step pyrolysis (NH3+Ar), due to the "etching effect" of ammonia gas and its ability to dope additional N elements into the catalyst; at the same time, the evaporation of Zn atoms at high temperature can provide holes to confine Mn atoms, then the first The catalyst after one step has enough defect nitrogen anchor sites and space to confine Mn ²⁺ . On the basis of the first step, the catalyst was mixed with a solution containing Mn ²⁺ (manganese acetate, manganese chloride, etc.) for secondary in-situ adsorption of Mn ²⁺ . "The catalyst prepared after the step is a catalyst of highly loaded Mn-N active site doped carbon material. The as-prepared catalyst has a higher loading of Mn-N active sites; meanwhile, the content of nitrogen atoms is also enhanced due to the NH treatment; the metal _- organic framework-derived carbon materials also have higher electrical conductivity, so the catalyst is suitable for many Sulfide has good catalytic and adsorption effect. When the catalyst is used as a separator modification material in lithium-sulfur batteries, it exhibits excellent specific capacity and outstanding cycle stability.

In order to achieve the above object, the technical scheme of the present invention is:

A highly loaded Mn-N active site-doped carbon catalyst, using Mn-ZIF-8 as a precursor, provides sufficient nitrogen atomic anchoring sites and spatial confinement for the catalyst through _NH3 atmosphere treatment and evaporation of Zn atoms. effect, and then prepare a highly loaded Mn-N site catalyst. The content of Mn atoms in the prepared catalyst was 2.31 wt% (ICP-MS), and the content of Mn-N bonds was as high as 11.75% (XPS).

A preparation method for preparing a highly loaded Mn-N active site doped carbon material catalyst, comprising the following steps:

Step 1: Synthesis of Mn-ZIF-8 precursor

Dissolve 2-methylimidazole in methanol solution, stir well to obtain solution A with a concentration of 1.0-1.4 mmol/mL; dissolve zinc nitrate hexahydrate and manganese acetate in methanol solution and stir well to obtain zinc nitrate hexahydrate and manganese acetate The concentrations of 0.18-0.22 mmol/mL and 0.04-0.06 mmol/mL of solution B, respectively. At room temperature, add solution B to an equal volume of solution A, stir slowly for 30-60 min, and leave for 20-26 h. The resulting precipitate is washed with ethanol for several times, and dried under vacuum at 60-80 °C for 12-16 h to obtain Mn- ZIF-8 precursor.

Step 2: Synthesis of low-loaded Mn-N active site-doped carbon material catalysts

The Mn-ZIF-8 precursor was pyrolyzed. First, the heating rate was controlled to be 3-5 °C/min in an argon atmosphere, and the temperature was raised to 750 °C for 0.5-1.5 h; Change to argon atmosphere and continue to heat up to 900-950℃ for 2.5h, then cool to room temperature naturally; the obtained product is stirred with 0.5mol/LH ₂ SO ₄ solution for 5-8h at 70-80℃ for pickling, The acid-washed material was washed with deionized water to neutrality (PH=7), and vacuum-dried at 60-80° C. for 12-16 h to obtain a low-loaded Mn-N active site-doped carbon material catalyst.

Step 3: Synthesis of highly loaded Mn-N active site doped carbon material catalyst

The catalyst obtained in the second step is dissolved in deionized water and ultrasonicated for 1.5-2 hours to form a uniformly dispersed suspension, and a manganese ion-containing compound is added to the solution to provide manganese ions, wherein the mass of the manganese ion compound is 1/1 of the mass of the catalyst. 4-1/3, the mixed solution was stirred for 2-3h. After the reaction is completed, the product is washed with deionized water for several times by suction filtration, vacuum dried at 60-80 °C for 12-16 hours, and the obtained powder sample is heated from room temperature to 900-950 °C in an argon atmosphere for 2.5-3 hours. The final product was obtained after an acid wash step after cooling to room temperature.

The manganese ion-containing compounds described in the third step are manganese acetate and manganese chloride.

The temperature increase rate described in the third step is 3-5°C/min.

The acid washing described in the third step is to use a 0.5mol/LH ₂ SO ₄ solution to stir for 5-8h at 70-80°C.

An application of a highly loaded Mn-N active site doped carbon material catalyst on a lithium-sulfur battery, the synthesized catalyst is used to modify a commercial lithium-sulfur battery PP separator, and is applied to a lithium-sulfur battery. The specific operation steps are:

Step 1: Preparation of the modified diaphragm

The prepared catalyst and the binder (PVDF) were mixed with a mass ratio of 9:1 and thoroughly ground. The obtained mixture was added with NMP and stirred at room temperature for 12 h to obtain a catalyst slurry. The catalyst slurry was scraped on the PP membrane at 60°C. Dry for 12h.

Step 2: Preparation of Sulfur/Carbon Cathode

The sublimated sulfur and carbon black were fully ground at a mass ratio of 7:3 and kept at 155 °C for 12 h in an Ar atmosphere. The obtained powder was mixed with Super P and PVDF according to the mass ratio of 7:2:1 and fully ground, and then NMP was added and stirred for 12h. The obtained uniformly mixed slurry was blade-coated on aluminum foil (the sulfur loading was adjusted by blade coating thickness), and dried at 60° C. for 12 h.

Step 3: Assemble the Lithium Sulfur Battery

The prepared composite separator, sulfur/carbon positive electrode and lithium sheet were assembled into a lithium-sulfur battery. The amount of electrolyte added on the positive side was 25 μL, the amount added on the negative side was 15 μL, and the sulfur loading was ~1.2 mg/cm ² .

The beneficial effects of the present invention are:

1) The raw materials for the preparation of the catalyst are cheap and easy to obtain. On this basis, the process can effectively increase the Mn-N active site and the loading of nitrogen atoms on the carbon material, so it has a good profit effect.

2) The prepared catalyst first adopts the "in-situ doping" process, and then adopts the "in-situ adsorption" process. The entire process flow adopts in-situ preparation of defects, and does not involve the removal process of the coating layer and the template, which can be used for the subsequent catalyst. The performance optimization provides a good guarantee.

3) The high loading of Mn-N active sites and defective N atoms in the catalyst can effectively improve the conversion rate of polysulfides in lithium-sulfur batteries. "shuttle effect", confines polysulfides to the cathode region and protects the lithium anode; on the other hand, metal-organic framework (MOF)-derived carbon materials as carriers of active sites can inherit the advantages of high specific surface area of MOF materials, and at the same time have excellent The conductivity can improve the utilization rate of sulfur element and discharge products (Li ₂ S/Li ₂ S ₂ ).

4) When the catalyst is applied as a separator modification material to a lithium-sulfur battery, the specific capacity and cycle stability of the lithium-sulfur battery can be effectively improved.

Description of drawings

Fig. 1 is the scanning electron microscope (SEM) picture of the catalyst prepared by embodiment 1;

Fig. 2 is the result diagram after the XPS N 1s peak fitting of the catalyst prepared in Example 1;

Figure 3 shows the rate performance of the catalyst prepared in Example 1 applied to a lithium-sulfur battery;

Figure 4 shows the cycle performance of the catalyst prepared in Example 1 applied to a lithium-sulfur battery;

FIG. 5 is a flow chart of preparing a highly loaded Mn-N site-doped carbon catalyst according to the present invention.

Specific implementation cases

The following is a further description of the preparation method of the highly loaded Mn-N active site catalyst through specific examples.

Implementation case 1 (the schematic diagram of the preparation process is shown in Figure 5):

The first step is to synthesize the Mn-ZIF-8 precursor

Take 30 mL of methanol solution A with 2-methylimidazole concentration of 1.2 mmol/ml; take zinc nitrate hexahydrate and manganese acetate, add 30 mL of methanol to make the two concentrations respectively 0.2 mmol/ml and 0.05 mmol/ml, and stir for 30 min to obtain solution B. At room temperature, solution B was added to solution A, and after slow stirring for 50 min, the precipitate obtained by standing for 24 h was washed with ethanol for several times, and dried under vacuum at 70 °C for 14 h to obtain the Mn-ZIF-8 precursor.

The second step is to synthesize low-loaded Mn-N active site catalysts

The Mn-ZIF-8 precursor was pyrolyzed. First, the heating rate was controlled to be 5 °C/min in an argon atmosphere, and the temperature was raised to 750 °C for 1 h; then, ammonia gas was introduced to maintain a constant temperature for 1.5 h, and then the argon atmosphere was replaced to continue. After warming up to 950°C for 2.5h, it was naturally cooled to room temperature; the obtained product was stirred at 80°C with 0.5mol/L H ₂ SO ₄ solution for 5h to pickle (the ratio of H ₂ SO ₄ solution to catalyst was 1 mg/L H 2 SO 4 ) mL), the acid-washed material was washed with deionized water to neutrality (PH=7), and vacuum-dried at 70 °C for 14 h to obtain a low-loaded Mn-N active site-doped carbon material catalyst.

The third step is to synthesize highly loaded Mn-N active site catalysts

The catalyst obtained in the second step was dissolved in deionized water and sonicated for 1.5h to form a uniformly dispersed suspension, manganese acetate was added to the solution, and the mass of the added manganese acetate was 1/4 of the catalyst mass, and the mixed solution was stirred for 2h. After the reaction was completed, the product was washed with deionized water by suction filtration for several times, dried under vacuum at 70 °C for 14 h, and the obtained powder sample was heated to 900 °C in an argon atmosphere for pyrolysis for 2.5 h (heating rate of 5 °C/min), and cooled. After reaching room temperature, the final product was obtained after acid washing (with 0.5 mol/L H ₂ SO ₄ solution stirring for 5 h at 80° C.).

The morphology of the prepared catalyst is shown in Figure 1. After different post-treatments, the morphology of ZIF-8 is still maintained, and the surface of the sample is rough due to the "etching" effect of ammonia gas treatment. At the same time, in order to show the content of Mn-N active sites and N atoms in the sample, XPS test was carried out (as shown in Figure 2). After fitting and calculation, the content of Mn-N bond, pyridine nitrogen and pyrrolic nitrogen in the sample They are: 11.75%, 28.98% and 20.74%, respectively, indicating that the samples have higher content of Mn-N active sites and defective nitrogen atoms to catalyze polysulfide conversion and limit its "shuttle effect".

The fourth step, the application of the obtained catalyst on lithium-sulfur batteries

To prepare the modified diaphragm:

The prepared catalyst and the binder (PVDF) were mixed with a mass ratio of 9:1 and thoroughly ground. The obtained mixture was added with NMP and stirred at room temperature for 12 h to obtain a catalyst slurry. The catalyst slurry was scraped on the PP membrane at 60°C. Dry for 12h.

Preparation of sulfur/carbon cathode:

The sublimated sulfur and carbon black were fully ground at a mass ratio of 7:3 and kept at 155 °C for 12 h in an Ar atmosphere. The obtained powder was mixed with Super P and PVDF according to the mass ratio of 7:2:1 and fully ground, and then NMP was added and stirred for 12h. The obtained uniformly mixed slurry was blade-coated on aluminum foil (the sulfur loading was adjusted by blade coating thickness), and dried at 60° C. for 12 h.

Assembling the lithium-sulfur battery:

The prepared composite separator, sulfur/carbon positive electrode and lithium sheet were assembled into a lithium-sulfur battery. The amount of electrolyte added on the positive side was 25 μL, the amount added on the negative side was 15 μL, and the sulfur loading was ~1.2 mg/cm ² .

The assembled lithium-sulfur battery was used for electrochemical performance test, and the results are shown in Figure 3 and Figure 4. When the current density is 0.1C, the specific capacity of the battery in the first cycle is as high as 1596mAh/g; when the current density rises to 2C, the specific capacity of the battery remains at 581mAh/g; at the current density of 0.5C, the cycle is 200 cycles After that, the specific volume retention rate was 91.0%. Rate tests and cycling stability tests show that the as-prepared catalysts have good electrical conductivity and ability to confine/catalyze polysulfides.

Implementation case 2:

The first step is to synthesize the Mn-ZIF-8 precursor

Take 30 mL of methanol solution A with 2-methylimidazole concentration of 1.0 mmol/ml; take zinc nitrate hexahydrate and manganese acetate, add 30 mL of methanol to make the two concentrations respectively 0.18 mmol/ml and 0.04 mmol/ml, and stir for 30 min to obtain solution B. At room temperature, solution B was added to solution A, and after stirring slowly for 30 min, the precipitate obtained by standing for 20 h was washed with ethanol for several times, and dried under vacuum at 60 °C for 12 h to obtain the Mn-ZIF-8 precursor.

The second step is to synthesize low-loaded Mn-N active site catalysts

The Mn-ZIF-8 precursor was pyrolyzed. First, the heating rate was controlled to be 3 °C/min in an argon atmosphere, and the temperature was raised to 750 °C for 0.5 h. Then, ammonia gas was introduced to maintain a constant temperature for 1.5 h, and then replaced with an argon atmosphere. Continue to heat up to 900°C for 2.5h, then cool to room temperature naturally; the obtained product was stirred for 5h with 0.5mol/L H ₂ SO ₄ solution at 70° C. for pickling (the ratio of H ₂ SO ₄ solution to catalyst was 1 mg /mL), the acid-washed material was washed with deionized water to neutrality (PH=7), and vacuum-dried at 60 °C for 12 h to obtain a low-loaded Mn-N active site-doped carbon material catalyst.

The third step is to synthesize highly loaded Mn-N active site catalysts

The catalyst obtained in the second step was dissolved in deionized water and ultrasonicated for 1.5h to form a uniformly dispersed suspension, manganese chloride was added to the solution, and the mass of the manganese chloride added was 1/4 of the mass of the catalyst, and the mixed solution was stirred for 2h . After the reaction was completed, the product was washed with deionized water by suction filtration for several times, dried under vacuum at 60°C for 12h, and the obtained powder sample was heated to 900°C in an argon atmosphere for pyrolysis for 2.5h (heating rate of 3°C/min), and cooled. After reaching room temperature, the final product was obtained after acid washing (with 0.5 mol/L H ₂ SO ₄ solution stirring for 5 h at 70° C.).

The fourth step, the application of the obtained catalyst on lithium-sulfur batteries

To prepare the modified diaphragm:

The prepared catalyst and the binder (PVDF) were mixed with a mass ratio of 9:1 and thoroughly ground. The obtained mixture was added with NMP and stirred at room temperature for 12 h to obtain a catalyst slurry. The catalyst slurry was scraped on the PP membrane at 60°C. Dry for 12h.

Preparation of sulfur/carbon cathode:

The sublimated sulfur and carbon black were fully ground at a mass ratio of 7:3 and kept at 155 °C for 12 h in an Ar atmosphere. The obtained powder was mixed with Super P and PVDF according to the mass ratio of 7:2:1 and fully ground, and then NMP was added and stirred for 12h. The obtained uniformly mixed slurry was blade-coated on aluminum foil (the sulfur loading was adjusted by blade coating thickness), and dried at 60° C. for 12 h.

Assembling the lithium-sulfur battery:

The prepared composite separator, sulfur/carbon positive electrode and lithium sheet were assembled into a lithium-sulfur battery. The amount of electrolyte added on the positive side was 25 μL, the amount added on the negative side was 15 μL, and the sulfur loading was ~1.2 mg/cm ² .

Implementation case 3:

The first step is to synthesize the Mn-ZIF-8 precursor

Take 30 mL of methanol solution A with 2-methylimidazole concentration of 1.4 mmol/ml; take zinc nitrate hexahydrate and manganese acetate, add 30 mL of methanol to make the two concentrations respectively 0.22 mmol/ml and 0.06 mmol/ml, and stir for 30 min to obtain solution B. At room temperature, solution B was added to solution A, and after stirring slowly for 60 min, the precipitate obtained by standing for 26 h was washed with ethanol for several times, and dried under vacuum at 80 °C for 16 h to obtain the Mn-ZIF-8 precursor.

The second step is to synthesize low-loaded Mn-N active site catalysts

The Mn-ZIF-8 precursor was pyrolyzed. First, the heating rate was controlled to be 5 °C/min in an argon atmosphere, and the temperature was raised to 750 °C for 1.5 h; then, ammonia gas was introduced for 2 h at a constant temperature, and then replaced with an argon atmosphere to continue. The temperature was raised to 950°C for 2.5h and then cooled to room temperature naturally; the obtained product was stirred for 8h with 0.5mol/L H ₂ SO ₄ solution at 80° C. for acid washing (the ratio of H ₂ SO ₄ solution to catalyst was 1.5mg /mL), the acid-washed material was washed with deionized water to neutrality (PH=7), and vacuum-dried at 80 °C for 16 h to obtain a low-loaded Mn-N active site-doped carbon material catalyst.

The third step is to synthesize highly loaded Mn-N active site catalysts

The catalyst obtained in the second step was dissolved in deionized water and sonicated for 2 hours to form a uniformly dispersed suspension, manganese acetate was added to the solution, and the mass of the added manganese acetate was 1/3 of the catalyst mass, and the mixed solution was stirred for 3 hours. After the reaction was completed, the product was washed with deionized water by suction filtration for several times, dried under vacuum at 80 °C for 16 h, and the obtained powder sample was heated to 950 °C in an argon atmosphere for pyrolysis for 2.5 h (heating rate of 5 °C/min), and cooled. After reaching room temperature, the final product was obtained after acid washing (with 0.5 mol/L H ₂ SO ₄ solution stirring for 8 h at 80° C.).

The fourth step, the application of the obtained catalyst on lithium-sulfur batteries

To prepare the modified diaphragm:

The prepared catalyst and the binder (PVDF) were mixed with a mass ratio of 9:1 and thoroughly ground. The obtained mixture was added with NMP and stirred at room temperature for 12 h to obtain a catalyst slurry. The catalyst slurry was scraped on the PP membrane at 60°C. Dry for 12h.

Preparation of sulfur/carbon cathode:

The sublimated sulfur and carbon black were fully ground at a mass ratio of 7:3 and kept at 155 °C for 12 h in an Ar atmosphere. The obtained powder was mixed with Super P and PVDF according to the mass ratio of 7:2:1 and fully ground, and then NMP was added and stirred for 12h. The obtained uniformly mixed slurry was blade-coated on aluminum foil (the sulfur loading was adjusted by blade coating thickness), and dried at 60° C. for 12 h.

Assembling the lithium-sulfur battery:

The prepared composite separator, sulfur/carbon positive electrode and lithium sheet were assembled into a lithium-sulfur battery. The amount of electrolyte added on the positive side was 25 μL, the amount added on the negative side was 15 μL, and the sulfur loading was ~1.2 mg/cm ² .

Implementation case 4:

The first step is to synthesize the Mn-ZIF-8 precursor

Take 30 mL of methanol solution A with 2-methylimidazole concentration of 1.0 mmol/ml; take zinc nitrate hexahydrate and manganese acetate, add 30 mL of methanol to make the two concentrations respectively 0.20 mmol/ml and 0.04 mmol/ml, and stir for 30 min to obtain solution B. At room temperature, solution B was added to solution A, and after stirring slowly for 60 min, the precipitate obtained by standing for 20 h was washed with ethanol for several times, and dried under vacuum at 60 °C for 16 h to obtain the Mn-ZIF-8 precursor.

The second step is to synthesize low-loaded Mn-N active site catalysts

The Mn-ZIF-8 precursor was pyrolyzed. First, the heating rate was controlled to be 3 °C/min in an argon atmosphere, and the temperature was raised to 750 °C for 1.5 h; then, ammonia gas was introduced to maintain a constant temperature for 1.5 h, and then replaced with an argon atmosphere. Continue to heat up to 950°C for 2.5h, then cool to room temperature naturally _; stir the obtained product with 0.5mol/L _H2SO4 solution for 8h at 70°C for pickling ₍ the ratio of _H2SO4 solution to catalyst is 1.5 mg/mL), the acid-washed material was washed with deionized water to neutrality (PH=7), and vacuum-dried at 60 °C for 16 h to obtain a low-loaded Mn-N active site-doped carbon material catalyst.

The third step is to synthesize highly loaded Mn-N active site catalysts

The catalyst obtained in the second step was dissolved in deionized water and ultrasonicated for 1.5h to form a uniformly dispersed suspension, manganese chloride was added to the solution, and the mass of the manganese chloride added was 1/4 of the mass of the catalyst, and the mixed solution was stirred for 3h . After the reaction was completed, the product was washed with deionized water for several times by suction filtration, dried under vacuum at 60 °C for 16 h, and the obtained powder sample was heated to 950 °C in an argon atmosphere for pyrolysis for 3 h (heating rate of 3 °C/min), and cooled to After room temperature, acid washing (with 0.5 mol/L H ₂ SO ₄ solution stirring for 8 h at 80° C.) was performed to obtain the final product.

The fourth step, the application of the obtained catalyst on lithium-sulfur batteries

To prepare the modified diaphragm:

The prepared catalyst and the binder (PVDF) were mixed with a mass ratio of 9:1 and thoroughly ground. The obtained mixture was added with NMP and stirred at room temperature for 12 h to obtain a catalyst slurry. The catalyst slurry was scraped on the PP membrane at 60°C. Dry for 12h.

Preparation of sulfur/carbon cathode:

The sublimated sulfur and carbon black were fully ground at a mass ratio of 7:3 and kept at 155 °C for 12 h in an Ar atmosphere. The obtained powder was mixed with Super P and PVDF according to the mass ratio of 7:2:1 and fully ground, and then NMP was added and stirred for 12h. The obtained uniformly mixed slurry was blade-coated on aluminum foil (the sulfur loading was adjusted by blade coating thickness), and dried at 60° C. for 12 h.

Assembling the lithium-sulfur battery:

The prepared composite separator, sulfur/carbon positive electrode and lithium sheet were assembled into a lithium-sulfur battery. The amount of electrolyte added on the positive side was 25 μL, the amount added on the negative side was 15 μL, and the sulfur loading was ~1.2 mg/cm ² .

The above-mentioned embodiments only represent the embodiments of the present invention, but should not be construed as a limitation on the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, which all belong to the protection scope of the present invention.

Claims (6)

1. the application of a highly loaded Mn-N active site doped carbon material catalyst in a lithium-sulfur battery, it is characterized in that, described catalyst is used for modifying lithium-sulfur battery PP diaphragm, the preparation method of described catalyst comprises The following steps: Step 1: Synthesis of Mn-ZIF-8 precursor Dissolve 2-methylimidazole in methanol solution and stir well to obtain solution A with a concentration of 1.0-1.4 mmol/mL; dissolve zinc nitrate hexahydrate and manganese acetate in methanol solution and stir well to obtain zinc nitrate hexahydrate and manganese acetate solution B with the concentrations of 0.18-0.22 mmol/mL and 0.04-0.06 mmol/mL respectively; at room temperature, add solution B to an equal volume of solution A, stir slowly for 30-60 min, and let stand for 20-26 h The obtained precipitate was washed with ethanol for many times, and dried in vacuum to obtain the Mn-ZIF-8 precursor; Step 2: Synthesis of low-loaded Mn-N active site-doped carbon material catalysts The Mn-ZIF-8 precursor was pyrolyzed. First, the heating rate was controlled to be 3-5 °C/min in an argon atmosphere, and the temperature was raised to 750 °C for 0.5-1.5 h; , continue to heat up to 900 – 950 °C for 2.5 h in an argon atmosphere, and then naturally cool to room temperature; the obtained product is stirred at 70 – 80 °C with H ₂ SO ₄ solution for 5-8 h for pickling, and the acid The washed material is washed with deionized water until neutral, and vacuum dried to obtain a low-loaded Mn-N active site doped carbon material catalyst; Step 3: Synthesis of highly loaded Mn-N active site doped carbon material catalyst The catalyst obtained in the second step is dissolved in deionized water, ultrasonically treated to obtain a uniformly dispersed suspension, and a manganese ion-containing compound is added to the solution to provide manganese ions, wherein the mass of the manganese ion compound is 1/4 of the mass of the catalyst. -1/3, stir the mixed solution for 2-3 h; after the reaction is completed, the product is washed with deionized water by suction filtration for several times, and after vacuum drying, the powder sample is heated from room temperature to 900-950 ℃ in an argon atmosphere for pyrolysis After 2.5-3 h, the final product was obtained after cooling to room temperature and acid washing. 2. The application of a highly loaded Mn-N active site doped carbon material catalyst in a lithium-sulfur battery according to claim 1, wherein the vacuum drying temperature is 60-80 °C, and the drying time is 60-80 °C. for 12-16 h. 3. The application of a highly loaded Mn-N active site doped carbon material catalyst in a lithium-sulfur battery according to claim 1, wherein the ultrasonic time in the third step is 1.5-2 h. 4. the application of a kind of high load Mn-N active site doped carbon material catalyst according to claim 1 in lithium-sulfur battery, it is characterized in that, the manganese ion-containing compound described in the 3rd step is manganese acetate, Manganese chloride. 5. The application of a highly loaded Mn-N active site-doped carbon material catalyst in a lithium-sulfur battery according to claim 1, wherein the temperature rise rate in the third step is 3-5 °C/ min. 6. The application of a highly loaded Mn-N active site-doped carbon material catalyst in a lithium-sulfur battery according to claim 1, wherein the acid washing described in the third step is performed at a temperature of 70-80 °C Use 0.5 mol/L H ₂ SO ₄ solution to stir for 5-8 h under conditions.

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