Preparation method and application of layered porous CoS-CoP@Co-NOC heterostructure composite material

Abstract

This invention discloses a method for preparing a layered porous CoS-CoP@Co-NOC heterojunction composite material, relating to the field of lithium-sulfur battery cathode materials. The method involves first preparing Co-MOFs via a solvothermal method, then modifying them with 3,4-dihydroxyphenylethylamine, mixing them with melamine, and finally subjecting them to high-temperature carbonization and oxidation to obtain nitrogen-oxygen co-doped layered Co-NOC. Simultaneously sulfiding and phosphating the layered Co-NOC yields the layered porous CoS-CoP@Co-NOC heterojunction composite material. The beneficial effects of this invention are that the obtained layered porous CoS-CoP@Co-NOC heterojunction composite material maintains the layered structure of Co-MOFs. When this material is loaded with sulfur and used as a cathode material in lithium-sulfur batteries, it enhances the redox reaction kinetics, improves the utilization rate of active materials, and enhances the cycle performance and stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery cathode materials technology, and in particular to a method for preparing a layered porous CoS-CoP@Co-NOC heterojunction composite material and its application. Background Technology

[0002] Currently, traditional lithium-ion batteries, due to their relatively low energy density, can no longer meet the growing demands of emerging electronic devices. Lithium / sulfur batteries, based on their higher theoretical energy density (2600Wh / kg) and larger theoretical specific capacity (1675mAh / g), are considered one of the most promising high-energy-density rechargeable battery systems. Furthermore, sulfur is abundant and inexpensive, and the sulfur electrode materials themselves and during use produce very few environmentally harmful substances. Therefore, lithium-sulfur batteries are a cheaper and more environmentally friendly option.

[0003] Despite the numerous advantages of lithium-sulfur batteries, their commercial application remains limited by several factors. These are primarily due to the low electronic and ionic conductivity of the active material sulfur and its discharge product lithium sulfide, resulting in poor electrode reaction kinetics and hindering the achievement of good rate performance. The dissolution of polysulfides in the liquid electrolyte generates a shuttle effect, inevitably leading to the loss of active electrode materials, while simultaneously causing self-discharge, capacity decay, and reduced coulombic efficiency. Furthermore, the volume changes of the sulfur cathode during charge and discharge cause pulverization and structural collapse of the electrode material, deteriorating the electrical contact between the electrode material and the current collector. Therefore, developing a suitable sulfur carrier to overcome the current shortcomings of lithium-sulfur batteries is crucial for improving their capacity and cycle performance.

[0004] To enhance the conductivity of sulfur in the cathode of lithium-sulfur batteries, reduce solvent migration of polysulfides, and improve the performance of lithium-sulfur batteries, research on cathode materials for lithium-sulfur batteries has received widespread attention. These studies mainly involve inorganic composite materials such as carbon materials, conductive polymers, and transition metal compounds as sulfur supports. Through strategies such as physical confinement and chemical adsorption, the shuttle movement of polysulfides has been suppressed to a certain extent, which has improved the performance of lithium-sulfur batteries. However, the problem of poor rate performance and cycle stability of lithium-sulfur batteries still exists. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention discloses a method for preparing a layered porous CoS-CoP@Co-NOC heterojunction composite material and its application. The material obtained by this method is a heterojunction composite material with CoS and CoP as the outer shell, encapsulating a Co core-shell structure, and covering the surface of a nitrogen-oxygen co-doped layered carbon framework. After loading sulfur onto this layered porous CoS-CoP@Co-NOC heterojunction composite material, it can be used as a cathode material in lithium-sulfur batteries. It can effectively adsorb polysulfides, enhance redox reaction kinetics, improve the utilization rate of active materials, and improve the cycle performance and stability of the battery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing layered porous CoS-CoP@Co-NOC heterojunction composite material involves dissolving cobalt salt and terephthalic acid in an organic solvent to prepare cobalt metal-organic frameworks (Co-MOFs) via a solvothermal method. Using these layered Co-MOFs as precursors, they are modified with 3,4-dihydroxyphenylethylamine to obtain DA-Co-MOFs with a 3,4-dihydroxyphenylethylamine surface coating. The DA-Co-MOFs are then mixed with melamine and subjected to high-temperature carbonization and oxidation to obtain nitrogen-oxygen co-doped layered Co-NOC. Finally, the layered Co-NOC is simultaneously mixed with elemental sulfur and phosphorus sources, followed by sulfidation and phosphating to obtain the layered porous CoS-CoP@Co-NOC heterojunction composite material.

[0008] Further, the preparation process of Co-MOFs is as follows: First, cobalt salt and terephthalic acid are dissolved in an organic solvent and reacted at 100-180℃ for 10-16h under stirring. The resulting purple suspension is filtered, and the collected solid is vacuum dried at 80-120℃ for 6-14h to obtain cobalt metal-organic frameworks (Co-MOFs).

[0009] Furthermore, the cobalt salt is selected from one of cobalt nitrate, cobalt chloride, and cobalt acetate, and the molar ratio of the cobalt salt to terephthalic acid is 2.5 to 1:1;

[0010] The organic solvent is selected from N,N-dimethylformamide, triethanolamine, and hexamethylenediamine, and the concentration of cobalt salt in the organic solvent is 0.13–0.33 mol / L.

[0011] Further, the preparation process of DA-Co-MOFs is as follows: Co-MOFs are dissolved in tris(hydroxymethyl)aminomethane buffer solution, 3,4-dihydroxyphenylethylamine is added under stirring, the reaction is carried out at room temperature for 10-12 h, centrifuged, and dried at 60 °C for 24 h to obtain DA-Co-MOFs with 3,4-dihydroxyphenylethylamine on the surface of Co-MOFs.

[0012] Furthermore, the pH of the tris(hydroxymethyl)aminomethane buffer solution was 8.1, the concentration of Co-MOFs in the tris(hydroxymethyl)aminomethane buffer solution was 58–136 g / L, and the mass ratio of Co-MOFs to 3,4-dihydroxyphenylethylamine was 2.4–1.5:1.

[0013] Further, the preparation process of Co-NOC is as follows: the obtained DA-Co-MOFs are mixed and ground with melamine, loaded into a ceramic boat, and heated to 700°C in a tube furnace under an argon atmosphere at a heating rate of 5°C / min. After carbonization and oxidation for 3 hours, the mixture is cooled to room temperature to obtain nitrogen-oxygen co-doped layered Co-NOC.

[0014] Furthermore, the mass ratio of DA-Co-MOFs to melamine is 1:0.5 to 2.

[0015] Further, the preparation process of the CoS-CoP@Co-NOC heterojunction composite material is as follows: a certain amount of Co-NOC, elemental sulfur and phosphorus source are weighed and ground for 30-60 min to mix evenly. Then, the mixture is placed in a ceramic boat and heated to 300-450℃ in an argon atmosphere in a tube furnace at a heating rate of 2℃ / min. The temperature is maintained for 3-5 h, and then cooled to room temperature. The obtained product is filtered and washed three times with deionized water. The solid is collected and vacuum dried at 60-100℃ for 10-14 h to obtain the sulfurized and phosphated layered porous CoS-CoP@Co-NOC heterojunction composite material.

[0016] Furthermore, the phosphorus source is selected from one of sodium hypophosphite, potassium hypophosphite, and ammonium hypophosphite, and the mass ratio of Co-NOC, elemental sulfur, and phosphorus source is 1:1.5 to 3:7 to 15.

[0017] Application of the layered porous CoS-CoP@Co-NOC heterojunction composite material prepared by the above method in the positive electrode active material of lithium-sulfur batteries.

[0018] The above-mentioned sulfur-loaded sulfur-containing positive electrode active material for lithium-sulfur batteries, based on the CoS-CoP@Co-NOC heterojunction composite material, is prepared by the following method:

[0019] Weigh out the CoS-CoP@Co-NOC heterojunction composite material and sublimed sulfur in a mass ratio of 3:7, grind for 30 min, and then transfer to a tube furnace for molten sulfur loading. Under an argon atmosphere, heat to 155℃ at a heating rate of 2℃ / min and hold for 14 h. Then heat to 180℃ and hold for 1 h, and then cool to room temperature to obtain the sulfur-loaded lithium-sulfur battery cathode active material.

[0020] This invention prepares cobalt metal-organic frameworks (Co-MOFs) via a solvothermal method. Using these layered Co-MOFs as precursors maintains the layered structure. When used as cathode materials for lithium-sulfur batteries, they can significantly increase the sulfur loading of the electrode, facilitate electrolyte transfer, and shorten the diffusion distance of ions.

[0021] After modification with 3,4-dihydroxyphenylethylamine, DA-Co-MOFs with 3,4-dihydroxyphenylethylamine-coated surfaces were obtained. Then, DA-Co-MOFs were mixed with melamine and subjected to high-temperature carbonization and oxidation to obtain nitrogen-oxygen co-doped layered Co-NOC. The layered surface was modified by 3,4-dihydroxyphenylethylamine and melamine. The carbon material derived from MOFs was rich in O and N elements, which improved the conductivity of the material and facilitated the high reactivity of sulfur.

[0022] Layered Co-NOC was then simultaneously mixed with elemental sulfur and phosphorus sources, followed by sulfidation and phosphating to obtain a layered porous CoS-CoP@Co-NOC heterojunction composite material. This material features a core-shell structure formed by cobalt sulfide and cobalt phosphide forming the outer shell and coating Co. The cobalt sulfide shell exhibits strong adsorption for polysulfides, while the cobalt phosphide catalyzes polysulfide conversion. This allows for rapid adsorption and conversion of intermediate polysulfide species generated at the sulfur cathode in lithium-sulfur batteries during charge and discharge on the CoS-CoP heterojunction surface, improving sulfur utilization and suppressing polysulfide shuttle. This material exhibits advantages such as good cycle stability and high specific capacity when applied to lithium-sulfur batteries.

[0023] The beneficial effects of this invention are:

[0024] (1) The CoS-CoP@Co-NOC heterojunction composite material prepared by this method maintains the layered structure of metal-organic frameworks (MOFs) well and can provide a larger specific surface area.

[0025] (2) The CoS-CoP@Co-NOC heterojunction composite material prepared by this method has abundant mesopores and micropores, which can not only load more elemental sulfur, but also limit the diffusion of polysulfides into the electrolyte, reduce the loss of active materials, and improve the electrochemical stability of sulfur electrode.

[0026] (3) The CoS-CoP@Co-NOC heterojunction composite material prepared by this method is a core-shell structure formed by coating Co with cobalt sulfide and cobalt phosphide as the outer shell. The cobalt sulfide in the outer shell has a strong adsorption effect on polysulfides, while the cobalt phosphide has a catalytic effect on the conversion of polysulfides. When used as a positive electrode active material for lithium-sulfur batteries, the intermediate species polysulfides generated during the charging and discharging process of the sulfur positive electrode of lithium-sulfur batteries can achieve rapid adsorption-diffusion-conversion on the surface of CoS-CoP heterojunction, which improves the utilization rate of sulfur and inhibits the shuttle of polysulfides.

[0027] (4) The carbon in the CoS-CoP@Co-NOC heterojunction composite material prepared by this method is derived from the organic ligands in the Co-MOF precursor through carbonization and then modified by nitrogen and oxygen co-doping, which changes the surface properties of carbon, enhances the conductivity and polarity of the composite material, improves the physical adsorption or chemical interaction force between polysulfide molecules, better restricts the dissolution of polysulfide ions, plays a good role in fixing the active substance sulfur, and creates favorable conditions for the rapid conversion of polysulfides.

[0028] (5) When the sulfur-loaded CoS-CoP@Co-NOC heterojunction composite material prepared by this method is used as a cathode material for lithium-sulfur batteries, it has high capacity, stable cycle performance and long life. Attached Figure Description

[0029] Figure 1 SEM image of nitrogen-oxygen co-doped layered Co-NOC prepared in Example 1;

[0030] Figure 2 SEM image of the CoS-CoP@Co-NOC heterojunction composite material prepared in Example 1;

[0031] Figure 3 The charge-discharge curves of the sulfur-loaded lithium-sulfur battery cathode material of the CoS-CoP@Co-NOC heterojunction composite material prepared in Example 4 are shown at a current density of 0.2C.

[0032] Figure 4 The cycling stability of the sulfur-loaded lithium-sulfur battery cathode material of the CoS-CoP@Co-NOC heterojunction composite material prepared in Example 4 at a current density of 0.2C.

[0033] Figure 5 The rate performance of the sulfur-loaded lithium-sulfur battery cathode material of the CoS-CoP@Co-NOC heterojunction composite material prepared in Example 4 from 0.1C to 1C. 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] This invention uses layered Co-MOFs as a precursor, which is modified with 3,4-dihydroxyphenylethylamine, then mixed with melamine, and then carbonized and oxidized at high temperature to obtain layered Co-NOC co-doped with O and N elements. Further, it is simultaneously sulfided and phosphated, so that the Co-NOC in the layered carbon layer is transformed into cobalt sulfide and cobalt phosphide on the surface, while the interior is a Co core-shell structure composite material.

[0036] First, cobalt salt and terephthalic acid were dissolved in an organic solvent to prepare cobalt metal-organic frameworks (Co-MOFs) via a solvothermal method. Using these layered Co-MOFs as precursors, they were modified with 3,4-dihydroxyphenylethylamine to obtain DA-Co-MOFs with 3,4-dihydroxyphenylethylamine coating. Then, the DA-Co-MOFs were mixed with melamine and subjected to high-temperature carbonization and oxidation to obtain nitrogen-oxygen co-doped layered Co-NOC. Finally, the layered Co-NOC was mixed with elemental sulfur and phosphorus sources, and after sulfidation and phosphating, a layered porous CoS-CoP@Co-NOC heterojunction composite material was obtained.

[0037] A method for preparing a layered porous CoS-CoP@Co-NOC heterostructure composite material, specifically including:

[0038] (1) Preparation process of Co-MOFs

[0039] Cobalt salt and terephthalic acid are dissolved in an organic solvent and reacted at 100–180 °C for 10–16 h under stirring. The resulting purple suspension is filtered, and the collected solid is vacuum dried at 80–120 °C for 6–14 h to obtain cobalt metal-organic frameworks (Co-MOFs).

[0040] The cobalt salt is selected from one of cobalt nitrate, cobalt chloride, and cobalt acetate, and the molar ratio of the cobalt salt to terephthalic acid is 2.5 to 1:1.

[0041] The organic solvent is selected from N,N-dimethylformamide, triethanolamine, and hexamethylenediamine, and the concentration of cobalt salt in the organic solvent is 0.13–0.33 mol / L.

[0042] (2) Preparation process of DA-Co-MOFs

[0043] The obtained Co-MOFs were dissolved in a tris(hydroxymethyl)aminomethane buffer solution, and 3,4-dihydroxyphenylethylamine was added under stirring. The reaction was carried out at room temperature for 10-12 h, centrifuged, and dried at 60 °C for 24 h to obtain DA-Co-MOFs with 3,4-dihydroxyphenylethylamine on the surface of the Co-MOFs.

[0044] The pH of the tris(hydroxymethyl)aminomethane buffer solution was 8.1, the concentration of Co-MOFs in the tris(hydroxymethyl)aminomethane buffer solution was 58–136 g / L, and the mass ratio of Co-MOFs to 3,4-dihydroxyphenylethylamine was 2.4–1.5:1.

[0045] (3) Preparation process of Co-NOC

[0046] The obtained DA-Co-MOFs were mixed and ground with melamine, loaded into a ceramic boat, and heated to 700°C in a tube furnace under an argon atmosphere at a heating rate of 5°C / min. After carbonization and oxidation for 3 hours, the mixture was cooled to room temperature to obtain nitrogen-oxygen co-doped layered Co-NOC.

[0047] The mass ratio of DA-Co-MOFs to melamine is 1:0.5 to 2.

[0048] (4) Preparation process of CoS-CoP@Co-NOC heterojunction composite material

[0049] A certain amount of Co-NOC, elemental sulfur, and phosphorus source were weighed separately, ground for 30-60 minutes to mix evenly, and then placed into a ceramic boat. The mixture was heated to 300-450℃ in an argon atmosphere in a tube furnace at a heating rate of 2℃ / min and held for 3-5 hours. After cooling to room temperature, the obtained product was filtered and washed three times with deionized water. The solid was collected and vacuum dried at 60-100℃ for 10-14 hours to obtain a layered porous CoS-CoP@Co-NOC heterojunction composite material after sulfurization and phosphating.

[0050] The phosphorus source is selected from one of sodium hypophosphite, potassium hypophosphite, and ammonium hypophosphite, and the mass ratio of Co-NOC, elemental sulfur, and phosphorus source is 1:1.5 to 3:7 to 15.

[0051] Example 1

[0052] (1) Preparation of Co-MOFs

[0053] 6.85 mmol of cobalt nitrate hexahydrate and 6.85 mmol of terephthalic acid were dissolved in 50 mL of N,N-dimethylformamide and reacted at 100 °C for 12 h under stirring to obtain a purple suspension. The purple suspension was filtered, and the collected solid was dried under vacuum at 100 °C for 12 h to obtain Co-MOFs.

[0054] (2) Preparation of DA-Co-MOFs

[0055] Weigh 5.8g of the Co-MOFs obtained in (1) above and dissolve it in 100mL of tris(hydroxymethyl)aminomethane buffer solution (pH=8.1). Add 2.9g of 3,4-dihydroxyphenylethylamine under stirring. React at room temperature for 12h, centrifuge, and dry at 60℃ for 24h to obtain DA-Co-MOFs.

[0056] (3) Preparation of Co-NOC

[0057] Weigh 1g of the product DA-Co-MOFs obtained in (2) above and mix and grind it with 0.5g of melamine. Place it in a porcelain boat and carbonize it in a tube furnace at 700℃ for 3h under an argon atmosphere. The heating rate is 5℃ / min. Cool it to room temperature to obtain Co-NOC.

[0058] (4) Preparation of CoS-CoP@Co-NOC heterojunction composite material: Weigh the above Co-NOC, elemental sulfur and sodium hypophosphite in a mass ratio of 1:2:10, grind them in a mortar for 30 min and mix them evenly. Put them into a porcelain boat and heat them in a tube furnace in an argon atmosphere to 350℃ at a heating rate of 2℃ / min. Hold the temperature for 3 h and cool to room temperature. Filter the obtained product and wash it three times with deionized water. The collected solid is vacuum dried at 60℃ for 12 h to obtain the CoS-CoP@Co-NOC heterojunction composite material.

[0059] Example 2

[0060] (1) Preparation of Co-MOFs

[0061] 6.85 mmol of cobalt chloride hexahydrate and 6.85 mmol of terephthalic acid were dissolved in 50 mL of N,N-dimethylformamide and reacted at 100 °C for 12 h under stirring to obtain a purple suspension. The purple suspension was filtered, and the collected solid was dried under vacuum at 110 °C for 12 h to obtain Co-MOFs.

[0062] (2) Preparation of DA-Co-MOFs

[0063] Weigh 5.8g of the Co-MOFs obtained in (1) above and dissolve it in 100mL of tris(hydroxymethyl)aminomethane buffer solution (pH=8.1). Add 2.9g of 3,4-dihydroxyphenylethylamine under stirring. React at room temperature for 12h, centrifuge, and dry at 60℃ for 24h to obtain DA-Co-MOFs.

[0064] (3) Preparation of Co-NOC

[0065] Weigh 1g of the product DA-Co-MOFs obtained in (2) above, mix and grind with 1g of melamine, put into a porcelain boat, and carbonize in a tube furnace at 700℃ for 3h under an argon atmosphere. The heating rate is 5℃ / min. Cool to room temperature to obtain Co-NOC.

[0066] (4) Preparation of CoS-CoP@Co-NOC heterojunction composite material

[0067] Weigh the above Co-NOC, elemental sulfur, and potassium hypophosphite in a mass ratio of 1:1.5:10, grind them in a mortar for 30 minutes to mix them evenly, put them into a porcelain boat, and heat them to 400℃ in an argon atmosphere in a tube furnace at a heating rate of 2℃ / min for 3 hours. After cooling to room temperature, filter the obtained product and wash it three times with deionized water. The collected solid was vacuum dried at 60℃ for 12 hours to obtain the CoS-CoP@Co-NOC heterojunction composite material.

[0068] Example 3

[0069] (1) Preparation of Co-MOFs

[0070] 13.70 mmol of cobalt nitrate hexahydrate and 6.85 mmol of terephthalic acid were dissolved in N,N-dimethylformamide and reacted at 120 °C for 12 h under stirring to obtain a purple suspension. The purple suspension was filtered, and the collected solid was dried under vacuum at 100 °C for 12 h to obtain Co-MOFs.

[0071] (2) Preparation of DA-Co-MOFs

[0072] Weigh 13.6g of the Co-MOFs obtained in (1) above and dissolve it in 100mL of tris(hydroxymethyl)aminomethane buffer solution (pH=8.1). Add 9.07g of 3,4-dihydroxyphenylethylamine under stirring. React at room temperature for 10h, centrifuge, and dry at 60℃ for 24h to obtain DA-Co-MOFs.

[0073] (3) Preparation of Co-NOC

[0074] Weigh 1g of the product DA-Co-MOFs obtained in (2) above, mix and grind with 2g of melamine, put into a porcelain boat, and carbonize in a tube furnace at 700℃ for 3h under an argon atmosphere. The heating rate is 5℃ / min. Cool to room temperature to obtain Co-NOC.

[0075] (4) Preparation of CoS-CoP@Co-NOC heterojunction composite material

[0076] Weigh the above Co-NOC, elemental sulfur, and sodium phosphite in a mass ratio of 1:2:15, grind them in a mortar for 30 minutes to mix them evenly, put them into a porcelain boat, and heat them in a tube furnace under an argon atmosphere to 350℃ at a heating rate of 2℃ / min for 3 hours. After cooling to room temperature, filter the obtained product and wash it three times with deionized water. The collected solid was vacuum dried at 60℃ for 12 hours to obtain the CoS-CoP@Co-NOC heterojunction composite material.

[0077] Example 4

[0078] (1) Preparation of Co-MOFs

[0079] 6.85 mmol of cobalt chloride hexahydrate and 6.85 mmol of terephthalic acid were dissolved in 50 mL of triethanolamine and reacted at 100 °C for 12 h under stirring to obtain a purple suspension. The purple suspension was filtered, and the collected solid was dried under vacuum at 80 °C for 12 h to obtain Co-MOFs.

[0080] (2) Preparation of DA-Co-MOFs

[0081] Weigh 13.6 g of the Co-MOFs obtained in (1) above and dissolve it in 100 mL of tris(hydroxymethyl)aminomethane buffer solution (pH = 8.1). Add 9.07 g of 3,4-dihydroxyphenylethylamine under stirring. React at room temperature for 10 h, centrifuge, and dry at 60 °C for 24 h to obtain DA-Co-MOFs.

[0082] (3) Preparation of Co-NOC

[0083] Weigh 1 g of the product DA-Co-MOFs obtained in (2) above and mix and grind it with 1 g of melamine. Put it into a porcelain boat and carbonize it in a tube furnace at a heating rate of 5 °C / min to 700 °C for 3 h under an argon atmosphere. Cool it to room temperature to obtain Co-NOC.

[0084] (4) Preparation of CoS-CoP@Co-NOC heterojunction composite material

[0085] Weigh the above Co-NOC, elemental sulfur, and sodium phosphite in a mass ratio of 1:2:15, grind them in a mortar for 30 minutes to mix them evenly, put them into a porcelain boat, and heat them to 400℃ in a tube furnace under an argon atmosphere at a heating rate of 2℃ / min. Hold the temperature for 3 hours, cool to room temperature, filter the obtained product, wash it three times with deionized water, and dry the collected solid under vacuum at 60℃ for 12 hours to obtain the CoS-CoP@CoO-NOC heterojunction composite material.

[0086] Application Example 1

[0087] The CoS-CoP@Co-NOC heterojunction composite material obtained in Example 4 was mixed with sublimed sulfur at a mass ratio of 7:3, and the mixture was kept at 155°C for 12 hours using a melt method to prepare a sulfur-loaded lithium-sulfur battery cathode material (sulfur cathode active material) based on the CoS-CoP@Co-NOC heterojunction composite material.

[0088] The sulfur positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1 to form a uniform slurry. The slurry was then uniformly coated onto the current collector aluminum foil using a wet film coater and dried at 60°C for 12 hours. Finally, the slurry was cut into circular electrode sheets with a diameter of 12 mm.

[0089] A circular electrode was used as the positive electrode, a lithium sheet as the negative electrode, and a Celgard 2400 polypropylene membrane with a diameter of 16 mm was used as the separator. The electrolyte was a mixed solution of 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with 1% LiNO3 added and ethylene glycol dimethyl ether (DME) / 1,3-dioxolane (DOL) (volume ratio of 1:1). The button cell of model CR2025 was assembled in a glove box filled with high-purity argon gas.

[0090] The charge and discharge performance of the assembled button batteries was tested using a battery tester, such as... Figure 3 and Figure 4 As shown, where, Figure 3 The charge-discharge curves of the sulfur-loaded lithium-sulfur battery cathode material prepared from the CoS-CoP@Co / NOC heterojunction composite material are shown at a current density of 0.2C. It can be seen that at a current density of 0.2C, the first-cycle discharge capacity of the battery reaches 1421 mAh g⁻¹. -1 .

[0091] Figure 4 The cycling stability of the sulfur-loaded lithium-sulfur battery cathode material, the prepared CoS-CoP@Co-NOC heterojunction composite material, was investigated at a current density of 0.2C. It was found that after 200 cycles at a current density of 0.5C, the capacity decay rate per cycle was 0.193%, and after 100 cycles, the CoS-CoP-C@S still retained 803.5 mAh g⁻¹. -1 The specific discharge capacity.

[0092] Application Example 2

[0093] The CR2025 button cell assembled according to the method in Application Example 1 was tested using a battery tester at charge and discharge rates of 0.1C, 0.2C, 0.5C, and 1.0C. The rate performance curves are shown below. Figure 5 As shown. Figure 5In the figure, the specific discharge capacities of the battery at rates of 0.1C, 0.2C, 0.5C, and 1.0C were 1413.8, 1287.3, 1188.5, and 1123.4 mAh·g, respectively. -1 After five charge-discharge cycles at 1.0C and then returning to a 0.2C rate, the battery still maintains 1127.9 mAh·g. -1 Its high discharge specific capacity demonstrates excellent rate performance.

[0094] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a layered porous CoS-CoP@Co-NOC heterojunction composite material, wherein the heterojunction composite material can be used as a battery cathode, characterized in that, Cobalt metal-organic frameworks (Co-MOFs) were prepared by dissolving cobalt salt and terephthalic acid in an organic solvent and then using a solvothermal method. Using these layered Co-MOFs as precursors, they were modified with 3,4-dihydroxyphenylethylamine to obtain DA-Co-MOFs with a 3,4-dihydroxyphenylethylamine-coated surface. Then, the DA-Co-MOFs were mixed with melamine and subjected to high-temperature carbonization and oxidation to obtain nitrogen-oxygen co-doped layered Co-NOC. Finally, the layered Co-NOC was mixed with elemental sulfur and phosphorus sources, and after sulfidation and phosphating, a layered porous CoS-CoP@Co-NOC heterojunction composite material was obtained.

2. The method for preparing the layered porous CoS-CoP@Co-NOC heterojunction composite material as described in claim 1, characterized in that, The preparation process of Co-MOFs is as follows: First, cobalt salt and terephthalic acid are dissolved in an organic solvent and reacted at 100-180℃ for 10-16 h under stirring. The resulting purple suspension is filtered, and the collected solid is vacuum dried at 80-120℃ for 6-14 h to obtain cobalt metal-organic frameworks (Co-MOFs).

3. The method for preparing the layered porous CoS-CoP@Co-NOC heterojunction composite material as described in claim 2, characterized in that, The cobalt salt is selected from one of cobalt nitrate, cobalt chloride, and cobalt acetate, and the molar ratio of the cobalt salt to terephthalic acid is 2.5 to 1:

1. The organic solvent is selected from N,N-dimethylformamide, triethanolamine, and hexamethylenediamine, and the concentration of cobalt salt in the organic solvent is 0.13–0.33 mol / L.

4. The method for preparing the layered porous CoS-CoP@Co-NOC heterojunction composite material as described in claim 1, characterized in that, Preparation process of DA-Co-MOFs: Co-MOFs were dissolved in tris(hydroxymethyl)aminomethane buffer solution, and 3,4-dihydroxyphenylethylamine was added under stirring. The reaction was carried out at room temperature for 10-12 h, centrifuged, and dried at 60 °C for 24 h to obtain DA-Co-MOFs with 3,4-dihydroxyphenylethylamine on the surface of Co-MOFs.

5. The method for preparing the layered porous CoS-CoP@Co-NOC heterojunction composite material as described in claim 4, characterized in that, The pH of the tris(hydroxymethyl)aminomethane buffer solution was 8.1, the concentration of Co-MOFs in the tris(hydroxymethyl)aminomethane buffer solution was 58–136 g / L, and the mass ratio of Co-MOFs to 3,4-dihydroxyphenylethylamine was 2.4–1.5:

1.

6. The method for preparing the layered porous CoS-CoP@Co-NOC heterojunction composite material as described in claim 1, characterized in that, Preparation process of Co-NOC: The obtained DA-Co-MOFs are mixed and ground with melamine, loaded into a ceramic boat, and heated to 700 °C in a tube furnace under an argon atmosphere at a heating rate of 5 °C / min. After carbonization and oxidation for 3 h, the mixture is cooled to room temperature to obtain nitrogen-oxygen co-doped layered Co-NOC.

7. The method for preparing the layered porous CoS-CoP@Co-NOC heterojunction composite material as described in claim 6, characterized in that, The mass ratio of DA-Co-MOFs to melamine is 1:0.5 to 2.

8. The method for preparing the layered porous CoS-CoP@Co-NOC heterojunction composite material as described in claim 1, characterized in that, Preparation process of CoS-CoP@Co-NOC heterojunction composite material: Weigh a certain amount of Co-NOC, elemental sulfur and phosphorus source, grind them for 30-60 min and mix them evenly. Then put them into a ceramic boat and heat them in a tube furnace under an argon atmosphere to 300-450℃ at a heating rate of 2℃ / min. Hold the temperature for 3-5 h and then cool to room temperature. Filter the obtained product and wash it three times with deionized water. Collect the solid and vacuum dry it at 60-100℃ for 10-14 h to obtain the sulfurized and phosphated layered porous CoS-CoP@Co-NOC heterojunction composite material.

9. The method for preparing the layered porous CoS-CoP@Co-NOC heterojunction composite material as described in claim 8, characterized in that, The phosphorus source is selected from one of sodium hypophosphite, potassium hypophosphite, and ammonium hypophosphite, and the mass ratio of Co-NOC, elemental sulfur, and phosphorus source is 1:1.5 to 3:7 to 15.

10. The application of the layered porous CoS-CoP@Co-NOC heterojunction composite material prepared by any one of the preparation methods described in claims 1-9 in the field of positive electrode active materials for lithium-sulfur batteries.

Images