CN114751393A - Nitrogen-sulfur co-doped porous carbon/sulfur composite material and preparation method and application thereof - Google Patents

Abstract

The invention provides a nitrogen and sulfur co-doped porous carbon/sulfur composite material and a preparation method thereof, wherein the preparation method comprises the following steps: s1: synthesizing a porous carbon material by adopting a soft template and hard template combined method and taking the soft template, the hard template and a carbon source as raw materials; s2: adding a nitrogen-sulfur source and carrying out nitrogen-sulfur double doping on the porous carbon material by adopting a hydrothermal method to synthesize a nitrogen-sulfur co-doped porous carbon material; s3: and mixing the prepared nitrogen-sulfur co-doped porous carbon material and elemental sulfur according to different mass proportions, grinding uniformly, and calcining in an inert gas atmosphere to obtain the nitrogen-sulfur co-doped porous carbon/sulfur composite material. The lithium-sulfur battery prepared by using the nitrogen-sulfur co-doped porous carbon/sulfur composite material as the cathode material has excellent electrochemical performance and self-discharge resistance when the lithium-sulfur battery has higher sulfur loading capacity.

Description

A nitrogen-sulfur co-doped porous carbon/sulfur composite material and its preparation method and application

technical field

The invention belongs to the technical field of lithium batteries, and in particular relates to a nitrogen-sulfur co-doped porous carbon/sulfur composite material and a preparation method and application thereof.

Background technique

Lithium-ion batteries are regarded as one of the most competitive electrochemical energy storage technologies due to their light weight, high specific energy/specific power, and long life, and are widely used in portable electronic communications and electric vehicles. Currently widely used cathode materials in lithium-ion batteries, such as LiCoO ₂ and LiFePO ₄ , have low theoretical capacities and cannot meet the needs of higher practical applications. Compared with traditional lithium-ion battery systems, lithium-sulfur (Li-S) batteries with elemental sulfur as the cathode have attracted much attention due to their high theoretical energy density, low cost, and no environmental pollution. As the electrode material, elemental sulfur has higher theoretical specific capacity (1675mAh g ^-1 ) and specific energy (2600Whkg ^-1 ). However, the lithium-sulfur battery itself also has some shortcomings: the electronic and ionic conductivity of elemental sulfur is relatively low at room temperature; the polysulfide intermediates generated during the electrochemical reaction of the lithium-sulfur battery are easily soluble in the organic electrolyte, causing the shuttle effect. ; The density of elemental S and its discharge product Li ₂ S are different, resulting in volume expansion, resulting in loss of active material. These problems lead to low sulfur utilization, poor battery cycle performance and rate performance, low coulombic efficiency, and severe self-discharge.

To solve these problems, the commonly used method is to combine sulfur with carbon materials, sulfides, metal organic frameworks, conductive polymers, metal oxides, etc., among which the most effective is to combine elemental sulfur with excellent electronic/ionic conductivity. Porous carbon material composite with rich pore structure. The use of porous carbon materials, on the one hand, improves the conductivity of elemental sulfur and its discharge products, and improves the utilization rate of active materials; Therefore, the diffusion of lithium polysulfide into the electrolyte can be inhibited and the shuttle effect of lithium polysulfide can be slowed down. Doping porous carbon materials with elements (O, P, N, S, B) can further improve the electrochemical performance of lithium-sulfur batteries because the doping elements have chemical adsorption on polysulfides. Higher sulfur content and sulfur loading will lead to more serious "shuttle effect", lower capacity, faster capacity fading and other problems. The loadings are generally low, and the self-discharge of lithium-sulfur batteries is rarely suppressed by designing porous carbon/sulfur composites. In addition, the preparation methods of most porous carbons are complicated and the cost of raw materials is relatively high, which is not conducive to the large-scale production of lithium-sulfur batteries.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a nitrogen-sulfur co-doped porous carbon/sulfur composite material and a preparation method thereof, so that the composite material has a higher sulfur content and an electrode sheet has a higher sulfur loading, and It is used as a cathode material for lithium-sulfur batteries, which enables lithium-sulfur batteries to have excellent electrochemical performance and resistance to self-discharge.

The technical scheme of the present invention is as follows: a preparation method of nitrogen-sulfur co-doped porous carbon/sulfur composite material is provided, comprising the following steps:

S1: A method of combining soft and hard templates is used to synthesize porous carbon materials with soft templates, hard templates and carbon sources as raw materials;

S2: adding a nitrogen-sulfur source and using a hydrothermal method to perform nitrogen-sulfur double doping on the above-mentioned porous carbon material to synthesize a nitrogen-sulfur co-doped porous carbon material;

S3: Mixing the prepared nitrogen-sulfur co-doped porous carbon material and elemental sulfur in different mass ratios, grinding uniformly, and calcining in an inert gas atmosphere to obtain a nitrogen-sulfur co-doped porous carbon/sulfur composite material.

The present invention is further provided that, in step S1, firstly, the hard template is pretreated in a tube furnace at 150-500° C. under air conditions, and ground into powder, and the carbon source and the soft template are added to anhydrous ethanol. , and the mass ratio of carbon source: soft template: absolute ethanol is (1-20): 1: (10-200), stir evenly to obtain a mixed solution; add the ground hard template powder to the mixed solution obtained above , continue to stir until uniform, wherein the ratio of the quality of the hard template to the sum of the quality of the carbon source and the soft template is 1:1 to 15; placing at room temperature allows the natural volatilization of absolute ethanol, and then in an oven at 50-200 ° C , heated and dried for 10-48h, and then calcined at 500-1200℃ for 1-10h in a tube furnace under Ar atmosphere; the obtained product was sequentially subjected to de-template treatment, suction filtration, washing and drying to obtain porous carbon material.

In the present invention, the heating rate is 0.2-10°C/min during the calcination process at 500-1200°C under the Ar atmosphere of the tube furnace.

The present invention is further provided that, in step S2, the porous carbon material prepared above is quantitatively weighed and uniformly mixed and dispersed into deionized water by ultrasonic waves, and the mass ratio of the porous carbon material to deionized water is 1:100-2000; Then add the nitrogen-sulfur source and continue stirring for 0.5-3h, and the mass ratio of the porous carbon material and the nitrogen-sulfur source is 1:5-15;

The mixed solution obtained above was transferred to a polytetrafluoroethylene hydrothermal kettle for hydrothermal reaction, and the reaction was carried out at 60-280 ° C for 1-28 h; after cooling to room temperature, the obtained mixed solution was centrifuged and washed with water for many times, and the reaction was carried out at 60 °C for 1-28 h. Bake in a vacuum oven at -100°C for 1-36 hours to obtain nitrogen-sulfur co-doped porous carbon materials.

The present invention is further provided that, in step S3, the prepared nitrogen-sulfur co-doped porous carbon material and elemental sulfur are mixed by ball milling, wherein the mass ratio of elemental sulfur is 10-95%; The nitrogen-sulfur co-doped porous carbon/sulfur composite was obtained by calcining at 50-300 °C for 1-48 h in an Ar atmosphere.

Preferably, the mass proportion of elemental sulfur is 60-95%.

The present invention further provides that, in step S1, the hard template is selected from any one of various types of crab shells; the soft template is selected from any one of CTAB, P123, F127, F108, and SDS.

The present invention further provides that, in step S1, the carbon source is selected from any one of sucrose, glucose, phenolic resin, furfuryl alcohol, and lignin.

The present invention further provides that, in step S2, the nitrogen-sulfur source is selected from any one of thiourea and amino-containing sulfonate.

The present invention also provides a nitrogen-sulfur co-doped porous carbon/sulfur composite material, the nitrogen-sulfur co-doped porous carbon/sulfur composite material is prepared according to the above preparation method.

The present invention also provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, the positive electrode material is the nitrogen-sulfur co-doped porous carbon/sulfur composite material prepared above, and the negative electrode is a lithium metal sheet.

When nitrogen-sulfur co-doped porous carbon/sulfur composites are used as cathode materials, the strong chemical bonds between nitrogen and sulfur atoms and polysulfides in nitrogen-sulfur co-doped porous carbon materials effectively inhibit the shuttle effect. The problems of poor cycle life, low Coulomb efficiency and serious self-discharge of lithium-sulfur batteries are improved.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The nitrogen-sulfur co-doped porous carbon material prepared according to the method of the present invention has a large specific surface area and excellent electrical conductivity.

(2) Using the nitrogen-sulfur co-doped porous carbon/sulfur composite material with high sulfur loading prepared by the method of the present invention as a positive electrode material to fabricate a lithium-sulfur battery, which still exhibits excellent electrochemical performance.

(3) The nitrogen-sulfur co-doped porous carbon/sulfur composite material prepared by the present invention is used in a lithium-sulfur battery. The nitrogen-sulfur co-doped porous carbon material has strong physical adsorption and chemical adsorption on polysulfides. It exhibits excellent anti-self-discharge behavior.

(4) The preparation method of the nitrogen-sulfur co-doped porous carbon/sulfur composite material of the present invention is simple, and the biomass material is used as the hard template raw material to prepare the double-doped porous carbon, the raw material source is wide, the cost is lower, and the The commercialization of lithium-sulfur batteries is of great significance.

Description of drawings

1 is a scanning electron microscope photograph of the nitrogen-sulfur co-doped porous carbon material described in Example 1.

FIG. 2 is the XPS pattern of the nitrogen-sulfur co-doped porous carbon material in Example 1. FIG.

FIG. 3 is a charge-discharge cycle curve of Example 1 based on the nitrogen-sulfur co-doped porous carbon/sulfur composite electrode in a lithium-sulfur battery.

FIG. 4 is a self-discharge study based on the nitrogen-sulfur co-doped porous carbon/sulfur composite electrode in a lithium-sulfur battery in Example 1.

FIG. 5 is a charge-discharge cycle curve of Example 2 based on the nitrogen-sulfur co-doped porous carbon/sulfur composite electrode in a lithium-sulfur battery.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The instruments used in the present invention include: cold field emission scanning electron microscope (FE-SEM S-4800), XSAM800 Ultra spectrometer, and LAND CT2001A type tester. The reagents used in the examples of the present invention are all commercially available products.

Example 1

First, the mud crab shells were pretreated in a tube furnace at 300°C under air conditions, and ground into powder. Add 1.2 g of phenolic resin and 0.6 g of CTAB to 50 mL of absolute ethanol, stir until the mixture is uniform, then add 1.2 g of the ground hard template, and continue to stir. The obtained solution was placed at room temperature to naturally volatilize anhydrous ethanol, then heated in an oven at 100 °C for 24 h, and finally calcined at 900 °C for 2 h in a tube furnace in an Ar atmosphere at a heating rate of 5 °C/min. The obtained product is treated with a hydrochloric acid solution to remove the template, and then suction filtered, washed and dried to obtain a porous carbon material.

First, 120 mg of the porous carbon material prepared above was uniformly dispersed into 80 mL of deionized water by ultrasonication, then 1.2 g of thiourea was added, and stirring was continued for 2 h. Then, the obtained mixed solution was transferred to a polytetrafluoroethylene hydrothermal kettle for hydrothermal reaction, and the reaction was carried out at 180° C. for 15 h. After cooling to room temperature, the obtained mixed solution was centrifuged for several times, washed with water, and dried in a vacuum oven at 70 °C for 12 h to obtain nitrogen-sulfur co-doped porous carbon materials, and the obtained nitrogen-sulfur co-doped porous carbon materials were characterized. . The specific surface area of the nitrogen-sulfur co-doped porous carbon material was measured to be 1200 m ² /g; a cold field emission scanning electron microscope (FE-SEM S-4800) was used to observe the nitrogen-sulfur co-doped porous carbon material prepared above. Figure 1 is the SEM picture of the nitrogen-sulfur co-doped porous carbon material. As shown in Figure 1, the prepared nitrogen-sulfur co-doped porous carbon material is mesoporous/macroporous hierarchical pores; X-ray photoelectron The elemental composition on the surface of the sample was characterized by energy spectrum analysis (XPS). The detection instrument was XSAM800Ultra spectrometer. The test results are shown in Figure 2. As shown in Figure 2, the two elements of nitrogen and sulfur were successfully doped into the carbon material.

The nitrogen-sulfur co-doped porous carbon material prepared above was mixed with elemental sulfur by ball milling, wherein the mass ratio of elemental sulfur was 80%, and then calcined at 155 °C for 18 h in an Ar atmosphere to obtain nitrogen-sulfur co-doped porous carbon materials. Carbon/Sulfur Composites.

The performance test of the nitrogen-sulfur co-doped porous carbon/sulfur composite material prepared above is carried out, and the specific steps are as follows:

(1) Preparation of positive electrode: The synthesized nitrogen-sulfur co-doped porous carbon/sulfur composite material, carbon black (Super P) and binder (PVDF) were mixed in a mass ratio of 8:1:1 and fully ground. Using N-methylpyrrolidone (NMP) as a dispersant, a uniform slurry with certain fluidity was obtained, and then the slurry was coated on a carbon-coated aluminum foil current collector and dried in a vacuum drying oven at 50 °C for 24 h.

(2) Battery charge and discharge performance test

The electrode sheet prepared by the composite material prepared in the above Example 1 was used as the positive electrode, the negative electrode used lithium sheet, the polymer film (PP, Celgard 2325) was used as the separator, and 1M _LiTFSI /DOL+DME (1 : 1, v/v) as the electrolyte, and all the above components were assembled into a 2016-type battery case in a glove box filled with Ar gas. The battery charge-discharge test temperature is 25°C, carried out on a LAND CT2001A tester, and the cut-off voltage of the charge-discharge test is 1.8-2.7V (vs. Li/Li ⁺ ). The sulfur content in the obtained composite material is as high as 80%, and the composite material is used as a raw material to prepare electrode sheets with a sulfur content of up to 4 mg·cm ^-2 . The charging and discharging test results of the battery are shown in Figure 3. The current density At 0.5C, the battery still showed excellent cycle performance.

(3) Battery self-discharge test: The lithium-sulfur battery based on the nitrogen-sulfur co-doped porous carbon/sulfur composite electrode was allowed to stand for up to a week, and then a charge-discharge test was performed, which was compared with the unstandby battery. Compare. Figure 4 shows the results of the charge-discharge test after being placed for a week. The results show that the battery prepared above basically has no self-discharge after being placed for a week, indicating that the lithium-sulfur battery prepared above has excellent anti-self-discharge performance.

Example 2

In this example, the prepared nitrogen-sulfur co-doped porous carbon material and elemental sulfur were mixed by ball milling, wherein the mass proportion of elemental sulfur was 60%, and other conditions were the same as those in Example 1; and the prepared nitrogen Sulfur co-doped porous carbon/sulfur composites were used as cathode materials to fabricate lithium-sulfur batteries for charge-discharge tests. The proportion of sulfur in the obtained composite material was 60%, and the composite material was used as a raw material to prepare an electrode sheet with a sulfur loading of 2 mg·cm ^-2 . The charge-discharge cycle curve of the battery is shown in Figure 5. With a current density of 0.5C, the battery exhibits excellent cycling performance.

Example 3

First, the mud crab shells were pretreated in a tube furnace at 300° C. under air conditions, and ground into powder. Add 1.2 g of sucrose and 0.8 g of CTAB to 80 mL of absolute ethanol, stir until the mixture is uniform, then add 1.5 g of the ground hard template, and continue to stir. The obtained solution was placed at room temperature to naturally volatilize anhydrous ethanol, then heated in an oven at 100 °C for 24 h, and finally calcined at 950 °C for 2 h in a tube furnace in an Ar atmosphere at a heating rate of 5 °C/min. The obtained product is treated with a hydrochloric acid solution to remove the template, filtered, washed and dried to obtain a porous carbon material.

First, 150 mg of the porous carbon material prepared above was uniformly dispersed into 80 mL of deionized water by ultrasonic, and then 1.5 g of thiourea was added, and stirring was continued for 2 h. Then, the obtained mixed solution was transferred to a polytetrafluoroethylene hydrothermal kettle for hydrothermal reaction, and the reaction was carried out at 190° C. for 15 h. After cooling to room temperature, the obtained mixed solution was centrifuged several times, washed with water, and dried in a vacuum oven at 60° C. for 12 h to obtain nitrogen-sulfur co-doped porous carbon materials.

The prepared nitrogen-sulfur co-doped porous carbon material and elemental sulfur were mixed by ball milling, wherein the mass ratio of elemental sulfur was 70%, and then calcined at 155 °C for 18 h in an Ar atmosphere to obtain nitrogen-sulfur co-doped porous carbon. /Sulfur composite. The nitrogen-sulfur co-doped porous carbon/sulfur composite material prepared in this example is used for lithium-sulfur batteries, the sulfur content in the composite material is 70%, and the loading amount of sulfur prepared by using the composite material as a raw material is 4 mg·cm ^{− 2} electrode sheets, and the prepared lithium-sulfur battery was tested, and the battery showed excellent cycle performance and low self-discharge.

Example 4

First, the swimming crab shells were pretreated in a tube furnace at 350°C under air conditions, and ground into powder. Add 1.2g of sucrose and 1.1g of P123 to 60mL of absolute ethanol, stir until the mixture is uniform, then add 1.5g of the ground hard template, and continue to stir. The resulting solution was left at room temperature to allow the ethanol to volatilize naturally. Then, it was heated in an oven at 100 °C for 24 h and dried, and finally calcined at 900 °C for 2 h in a tube furnace in an Ar atmosphere with a heating rate of 5 °C/min. The obtained product is subjected to de-template treatment, suction filtration, washing and drying to obtain a porous carbon material.

First, 150 mg of the porous carbon material prepared above was uniformly dispersed into 80 mL of deionized water by ultrasonic, and then 1.5 g of thiourea was added, and stirring was continued for 2 h. Then, the obtained mixed solution was transferred to a polytetrafluoroethylene hydrothermal kettle for hydrothermal reaction, and the reaction was carried out at 200° C. for 15 h. After cooling to room temperature, the obtained mixed solution was centrifuged several times, washed with water, and dried in a vacuum oven at 60° C. for 12 h to obtain nitrogen-sulfur co-doped porous carbon materials.

The prepared nitrogen-sulfur co-doped porous carbon material and elemental sulfur were mixed by ball milling, wherein the mass proportion of elemental sulfur was 80%, and then calcined at 155 °C for 18 h in an Ar atmosphere to obtain nitrogen-sulfur co-doped porous carbon /Sulfur composite. The nitrogen-sulfur co-doped porous carbon/sulfur composite material prepared in this example is used in lithium-sulfur batteries to prepare electrode sheets with a sulfur loading of 4 mg·cm ^-2 ; the prepared lithium-sulfur batteries are subjected to charge-discharge tests , the battery exhibits excellent cycle performance and low self-discharge.

Example 5

In this example, the pretreatment temperature of the hard template is 350° C., and the others are the same as in Example 1.

Example 6

In this embodiment, the soft template is P123, and others are the same as those in Embodiment 2.

Example 7

In the present embodiment, the nitrogen-sulfur source is sodium p-aminobenzenesulfonate, and the others are the same as those in embodiment 3.

The nitrogen-sulfur co-doped porous carbon materials prepared in Examples 5-7 also have good electrical conductivity. The prepared nitrogen-sulfur co-doped porous carbon/sulfur composite material is used for lithium-sulfur batteries, and the sulfur content in the composite material is as high as 80%, and the composite material is used as a raw material to prepare an electrode sheet with a sulfur loading of 4 mg·cm ^-2 , due to the strong chemisorption of polysulfides by nitrogen and sulfur atoms, the battery also exhibits excellent cycle performance and low self-discharge.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection of the present invention. within the range.

Claims (10)

1. a preparation method of nitrogen-sulfur co-doped porous carbon/sulfur composite material, is characterized in that, comprises the steps: S1: A method of combining soft and hard templates is used to synthesize porous carbon materials with soft templates, hard templates and carbon sources as raw materials; S2: adding a nitrogen-sulfur source and using a hydrothermal method to perform nitrogen-sulfur double doping on the above-mentioned porous carbon material to synthesize a nitrogen-sulfur co-doped porous carbon material; S3: Mixing the prepared nitrogen-sulfur co-doped porous carbon material and elemental sulfur in different mass ratios, grinding uniformly, and calcining in an inert gas atmosphere to obtain a nitrogen-sulfur co-doped porous carbon/sulfur composite material. 2 . The method for preparing a nitrogen-sulfur co-doped porous carbon/sulfur composite material according to claim 1 , wherein in step S1 , the hard template is first placed in a tube furnace at 150-500° C. under air conditions. 3 . Pre-treatment was carried out under the condition and ground into powder, and the carbon source and soft template were added to absolute ethanol, and the mass ratio of carbon source: soft template: absolute ethanol was (1～20):1:(10～200 ), stir to obtain a mixed solution; add the ground hard template powder to the above-obtained mixed solution, and continue to stir until uniform, wherein the ratio of the quality of the hard template to the quality sum of the carbon source and the soft template is 1 : 1 to 15; placed at room temperature to naturally volatilize anhydrous ethanol, then heated and dried in an oven at 50-200°C for 10-48h, and then calcined at 500-1200°C for 1-10h in a tube furnace under Ar atmosphere; The obtained product is sequentially subjected to de-template treatment, suction filtration, washing and drying to obtain a porous carbon material. 3. The preparation method of a nitrogen-sulfur co-doped porous carbon/sulfur composite material according to claim 2, wherein in the calcination process of 500-1200 DEG C under the Ar atmosphere of the tube furnace, the heating rate is 0.2 -10°C/min. 4. The preparation method of a nitrogen-sulfur co-doped porous carbon/sulfur composite material according to claim 1, wherein in step S2, the porous carbon material prepared above is quantitatively weighed and uniformly mixed and dispersed to In deionized water, the mass ratio of the porous carbon material to the deionized water is 1:100-2000; then the nitrogen-sulfur source is added to continue stirring for 0.5-3h, and the mass ratio of the porous carbon material and the nitrogen-sulfur source is 1:1: 5～15; The mixed solution obtained above was transferred to a polytetrafluoroethylene hydrothermal kettle for hydrothermal reaction, and the reaction was carried out at 60-280 ° C for 1-28 h; after cooling to room temperature, the obtained mixed solution was centrifuged and washed with water for many times, and the reaction was carried out at 60 °C for 1-28 h. Bake in a vacuum oven at -100°C for 1-36 hours to obtain nitrogen-sulfur co-doped porous carbon materials. 5. The method for preparing a nitrogen-sulfur co-doped porous carbon/sulfur composite material according to claim 1, wherein in step S3, the obtained nitrogen-sulfur co-doped porous carbon material and elemental sulfur are Mixing by ball milling, wherein the mass proportion of elemental sulfur is 10-95%, and then the mixture of the two is calcined at 50-300°C for 1-48h in an Ar atmosphere to obtain nitrogen-sulfur co-doped porous carbon/sulfur composite material; Preferably, the mass proportion of elemental sulfur is 60-95%. 6. The preparation method of a nitrogen-sulfur co-doped porous carbon/sulfur composite material according to claim 1, wherein in step S1, the hard template is selected from any of various types of crab shells ; The soft template is selected from any one of CTAB, P123, F127, F108, and SDS. 7. The method for preparing a nitrogen-sulfur co-doped porous carbon/sulfur composite material according to claim 1, wherein in step S1, the carbon source is selected from the group consisting of sucrose, glucose, phenolic resin, furfuryl alcohol, any of lignin. 8. The preparation method of nitrogen-sulfur co-doped porous carbon/sulfur composite material according to claim 1, wherein in step S2, the nitrogen-sulfur source is selected from thiourea, amino-containing sulfonic acid any kind of salt. 9 . A nitrogen-sulfur co-doped porous carbon/sulfur composite material, wherein the nitrogen-sulfur co-doped porous carbon/sulfur composite material is prepared according to the preparation method according to any one of claims 1 to 8 . 10. A lithium-sulfur battery, characterized in that it comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, the positive electrode material is the nitrogen-sulfur co-doped porous carbon/sulfur composite material according to claim 9, and the negative electrode is lithium Metal sheets.

Images