A metal atom (M)-non-metal element (N) porous material composite sulfur positive electrode material

Abstract

The application discloses a metal atom (M)-nonmetal element (N) porous material composite sulfur positive electrode material. The composite sulfur positive electrode material is a composite material obtained by loading metal atom (M)-nonmetal element (N) on a porous carrier, and further loading sulfur, sulfide and other sulfur-containing positive electrode materials to prepare a composite structure. The metal atom-nonmetal element structure composite sulfur positive electrode material developed by the application has the following structural characteristics and electrical performance characteristics: the metal atom-nonmetal element structure with high loading, high dispersion and high electrocatalytic activity can realize catalysis on the discharge and charging processes of the sulfur positive electrode, significantly improves the rapid conversion process of the sulfur-based positive electrode material, and is a high-activity and double-effect sulfur positive electrode catalyst.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to the structural design and construction of a sulfur cathode material with a composite structure of metal atoms and non-metal atoms (N / O / C / P). The composite sulfur cathode material exhibits high specific capacity and excellent cycle stability in lithium-sulfur batteries. Background Technology

[0002] Among high-energy-density battery systems, lithium-sulfur batteries represent the most practically applicable next-generation battery system, with a theoretical specific energy of 2600 Wh / kg and current practical batteries achieving 700 Wh / kg. However, the main bottleneck for current lithium-sulfur batteries lies in the dissolution and loss of polysulfides during charge-discharge reactions, and the shuttle effect, which leads to insufficient cycle stability to meet the requirements of various application technologies. Therefore, it is necessary to develop highly active sulfur-based composite materials that can significantly suppress polysulfide dissolution and loss and catalyze the electrochemical reactions of polysulfides, thereby improving the cycle life of lithium-sulfur batteries and ultimately preparing lithium-sulfur batteries with high cycle stability for practical application.

[0003] Currently, various carrier materials with physical adsorption and chemical bonding effects on lithium sulfide, such as oxides and porous carbon, are used to improve the adsorption performance of polysulfides. While this can suppress polysulfide loss to a certain extent, the conversion of lithium polysulfides to lithium sulfide is the rate-determining step in the electrochemical reaction of lithium-sulfur batteries. Adsorbed lithium polysulfides are difficult to rapidly convert into the final discharge product of sulfur-based materials, lithium sulfide, leading to the occupation of adsorption sites and the inability to achieve a rapid adsorption-conversion equilibrium at these sites, thus hindering the long lifespan of lithium-sulfur batteries. Therefore, it is necessary to develop novel composite sulfur cathode materials that can effectively adsorb and rapidly catalytically convert lithium polysulfides, while also exhibiting high structural stability. Summary of the Invention

[0004] Developing sulfur-based cathode materials with long-term cycle stability to improve the cycle life of lithium-sulfur batteries is an effective means to solve the technical bottlenecks faced by lithium-sulfur batteries in practical applications. This invention designs and develops a composite sulfur-based cathode structure with high electrochemical activity and high cycle stability, thereby significantly improving the cycle life of lithium-sulfur batteries. The purpose of this invention is to develop a bifunctional sulfur-based composite cathode material that can effectively adsorb polysulfides and accelerate their electrochemical conversion reactions. The core technology of this invention is: designing a porous support structure to achieve efficient dispersion of active sulfur-based materials and effective adsorption of polysulfides; simultaneously, utilizing the porous support to efficiently disperse highly electrocatalytically active components of metal atoms and non-metal elements (N / O / C / P), accelerating the electrochemical conversion reactions of adsorbed polysulfides through the electrocatalytically active components, achieving a continuous balance between adsorption and conversion of polysulfides in the composite sulfur cathode material, thereby significantly improving the cycle stability of the composite sulfur cathode material and thus increasing the cycle life of lithium-sulfur batteries.

[0005] A sulfur cathode material with a metal atom-nonmetal element (N / O / C / P) composite structure is characterized in that: the composite sulfur cathode material is a composite material obtained by loading a metal atom-nonmetal element (N / O / C / P) catalyst onto a porous support, and further prepared by highly dispersing elemental sulfur, sulfides and other sulfur-based cathode materials.

[0006] The metal atoms in the metal atom-nonmetal catalyst of the composite sulfur cathode of the present invention include one or more of Fe, Co, Cu, and Ni, and the particle size of the metal atoms is 0.01nm-0.05nm. In the composite sulfur cathode material, the mass percentage of metal atoms is 0.1wt.% to 10wt.%.

[0007] The porous support in the composite sulfur cathode of this invention comprises hollow mesoporous carbon spheres, carbon nanotubes, graphene, C3N4, doped porous carbon, etc. The specific surface area of ​​the porous support is 50–2000 m². 2 / g, the porous support surface contains functional groups such as N, O, C, P, etc.

[0008] The sulfur-based material in the composite sulfur cathode of the present invention is one or a mixture of two of the following: elemental sulfur, sulfurized polyacrylonitrile, polysulfide carbide, and organic sulfurized polymer, and the mass percentage of the sulfur-based material in the composite sulfur cathode material is 20 wt.% to 70 wt.%.

[0009] In the composite sulfur cathode material of the present invention, metal atoms are highly dispersed in a porous support. The N / O / C / P atomic groups on the surface of the porous support form strong chemical bonds with the metal atoms, thereby achieving high stability and high dispersion of the metal atoms.

[0010] The porous support in the composite sulfur cathode material of this invention has N / O / C / P functional groups on its surface that can capture free lithium polysulfides in the battery system through electrostatic interaction and physical adsorption, thereby achieving effective contact between metal atoms and polysulfides and realizing the electrocatalytic effect of metal atoms on polysulfides.

[0011] The preparation process of the composite sulfur cathode material of this invention includes: preparation of a porous support, surface modification of the porous support, effective bonding of the modified porous support with metal ions, and then preparation of a metal atom-N / C / O / P highly catalytically active structure through the bonding of functional groups such as N / O / C / P. The prepared composite structure is then used to support sulfur-based active materials, thereby preparing a sulfur cathode material with a metal atom M-non-metal element (N) composite structure. The electrocatalytic effect of the composite sulfur cathode material on the discharge intermediate product polysulfides includes: promoting the conversion reaction of lithium polysulfides to lithium sulfides, and also promoting the conversion reaction of lithium sulfides to sulfur-based cathodes, thus serving as a dual-effect catalyst for sulfur-based cathodes.

[0012] This invention discloses a sulfur cathode material with a metal atom (M)-non-metal element (N) composite structure, which is applied to lithium-sulfur batteries: In coin-type lithium-sulfur batteries, the specific capacity of the composite sulfur cathode material calculated based on sulfur-based materials is 1500mAh / g to 500mAh / g, and the cycle stability is greater than 1000 cycles; When applied to pouch lithium-sulfur batteries, the battery cycle life is significantly improved, and the cycle stability is greater than 200 cycles (capacity retention rate is greater than 90%).

[0013] The superiority of this invention lies in the fact that the sulfur cathode material with a composite structure of metal atoms (M) and non-metal elements (N) possesses a stable structure and highly efficient electrochemical properties. Its structural features are as follows: the porous support enables efficient dispersion of both the electrochemically active sulfur-based material and the electrocatalytically active metal atoms (M) and non-metal elements (N), while the unoccupied exposed surface of the porous support effectively adsorbs polysulfides. Corresponding to its structural characteristics, the composite sulfur cathode material exhibits the following significant electrochemical properties: The highly dispersed and tunable percentage of sulfur-based components enables the composite sulfur cathode material to achieve high specific capacity; the metal atom (M)-non-metal element (N) structural components possess a dual electrocatalytic effect on the electrochemical oxidation and reduction of sulfur-based materials, accelerating the electrochemical reaction rate of the rate-controlled reaction steps of sulfur-based materials, i.e., catalyzing the conversion reaction rate between polysulfides and lithium sulfide, and inhibiting the reduction in lithium-sulfur battery cycle life caused by polysulfide dissolution; the tunable surface limit of the porous support enables strong physical and chemical adsorption of polysulfides, combined with the highly efficient electrocatalytic effect of metal atom (M)-non-metal element (N) on polysulfides, achieving effective adsorption and rapid catalytic conversion of polysulfides by the composite structure, i.e., achieving a continuous balance between adsorption and conversion, and realizing high electrochemical activity of the composite sulfur cathode material, thereby significantly improving the cycle stability of the composite sulfur cathode material and thus improving the cycle life of lithium-sulfur batteries. Attached Figure Description

[0014] Figure 1 Aberration-corrected electron micrograph of the porous carbon-supported single-atom iron-N structure material prepared in Example 1. Detailed Implementation

[0015] Example 1:

[0016] Hollow carbon spheres were prepared according to the method described in the literature (Journal of Energy Chemistry 51(2020)262–271). The hollow inner diameter of the carbon spheres was 100 nm, the wall thickness was approximately 30 nm, and the sphere walls had mesoporous channels with an inner diameter of 2–4 nm perpendicular to the sphere surface, with a pore volume of 1.2 cm³. 3 / g. Using an argon / ammonia mixture (volume ratio 3:1), the temperature was increased to 600℃ at a rate of 5℃ / min and held at this temperature for 2 hours to obtain nitrogen-doped hollow carbon spheres. 0.1g of the nitrogen-doped hollow carbon spheres was ultrasonically dispersed in 50ml of ethanol, and 10ml of tetrahydrofuran solution containing 10mg of iron phthalocyanine was added. The mixture was stirred at room temperature for 3 hours, centrifuged, washed, dried, and then treated at 900℃ for 3 hours under an argon atmosphere to obtain a porous carbon support with a single-atom iron-N structure.

[0017] The prepared porous carbon spheres loaded with single iron atoms were subjected to argon atmosphere heat treatment at a mass ratio of 1:2 with sublimed sulfur at 155℃ for 10h and 300℃ for 2h to prepare a sulfur-carbon composite cathode material containing a single Fe-N structure (Fe mass percentage 1.5wt.%, N content 3wt.%, sulfur content 51wt.%, carbon content 44.5wt.%).

[0018] Take 0.09 g of hollow carbon-sulfur material and add 0.2 g of polyvinylidene fluoride (PVDF, 5% by mass) solution. Prepare a slurry (total solids content in the slurry is 20 wt.%) using N-methylpyrrolidone as solvent. After grinding for 1 hour, use a scraper to coat a 200-micron thick film onto carbon-coated aluminum foil. Dry at 60°C overnight, slice, weigh, and vacuum dry at 55°C for 24 hours. Use this electrode as the positive electrode and lithium sheet as the negative electrode. Celgard 250 Using 0 as the separator, 1M lithium bis(trifluoromethanesulfonyl)imide solution (LITFSI) as the electrolyte, 0.2M lithium nitrate as the additive, and a mixture of 1,3-dioxolane (DOL) and dimethyl ether (DME) (volume ratio 1:1) as the solvent, the battery was assembled and charged and discharged at 1C rate. The specific capacity of the first discharge cycle was 1006.1 mAh / g, and after 500 cycles, it still had a specific capacity of 929.7 mAh / g.

[0019] TEM images of the prepared porous carbon material supported on a single-atom Fe-N structure are attached. Figure 1 .

[0020] Comparative Example 1:

[0021] Hollow carbon spheres were prepared according to the method described in the literature (Journal of Energy Chemistry 51(2020)262–271). The hollow inner diameter of the carbon spheres was 100 nm, the wall thickness was approximately 30 nm, and the sphere walls had mesoporous channels of about 3 nm perpendicular to the sphere surface. Nitrogen-doped hollow carbon spheres were obtained by heating to 600 °C using an argon / ammonia mixture (volume ratio 3:1) at a rate of 5 °C / min and holding at that temperature for 2 h.

[0022] The prepared hollow carbon spheres and elemental sulfur were subjected to argon atmosphere heat treatment at a mass ratio of 1:2 at 155℃ for 10h and 300℃ for 2h to prepare sulfur-carbon composite cathode material.

[0023] The electrode coating was the same as in Example 1. The lithium-sulfur battery prepared in this comparative example had a first-cycle 1C charge-discharge capacity of 850.1 mAh / g and a capacity of 547.7 mAh / g after 500 cycles.

[0024] Comparative Example 2:

[0025] Hollow mesoporous carbon spheres were prepared according to the method in Example 1. The prepared hollow carbon spheres were then heat-treated with elemental sulfur at a mass ratio of 1:2 under an argon atmosphere at 155°C for 10 hours and 300°C for 2 hours to obtain a sulfur-carbon composite cathode material. An electrode was prepared according to the method in Comparative Example 1, and its initial 1C charge-discharge capacity was 834.1 mAh / g, but after 500 cycles, the capacity was only 235.2 mAh / g.

[0026] Example 2:

[0027] Hollow carbon spheres were prepared according to the method described in the literature (Journal of Energy Chemistry 51(2020)262–271). The hollow inner diameter of the carbon spheres was 100 nm, the wall thickness was approximately 30 nm, and the sphere walls had mesoporous channels of about 3 nm perpendicular to the sphere surface. Nitrogen-doped hollow carbon spheres were obtained by heating to 600 °C at a rate of 5 °C / min and holding the temperature for 2 h using an argon / ammonia mixture (volume ratio 2:1). 0.1 g of nitrogen-doped hollow carbon spheres were ultrasonically dispersed in 50 ml of ethanol, and 10 ml of tetrahydrofuran solution containing 10 mg of iron phthalocyanine was added. The mixture was stirred at room temperature for 3 h, centrifuged, washed, dried, and then treated at 900 °C for 2 h under an argon atmosphere to obtain a porous carbon support with a single-atom iron-N structure. According to the method for preparing carbon-sulfur composites in Example 1, porous carbon loaded with monatomic iron-N and sulfurized polyacrylonitrile were heat-treated at 150°C for 2 hours under a nitrogen atmosphere at a mass ratio of 1:1 to obtain a composite of porous carbon loaded with monatomic iron-N and sulfurized polyacrylonitrile (Fe mass percentage 2.1 wt.%, N content 4 wt.%, sulfur content 40 wt.%, carbon content 53.9 wt.%).

[0028] Example 3:

[0029] Commercially available 20-micron diameter multi-arm carbon nanotubes were purchased. 1 g of the multi-arm carbon nanotubes were added to 10 ml of 12 mol / L concentrated nitric acid and refluxed at 150°C for 2 h. After washing with water until neutral, the nanotubes were dried to obtain oxygen-containing carbon nanotubes. 0.1 g of the oxygen-containing carbon nanotubes were ultrasonically dispersed in 50 ml of ethanol, and 10 ml of ethanol solution containing 10 mg of cobalt acetate was added. The mixture was stirred at room temperature for 3 h, centrifuged, washed, dried, and then treated at 900°C for 3 h under an argon atmosphere to obtain a porous carbon support with a single-atom cobalt-O structure. The prepared porous carbon with a single-atom cobalt-O structure was then heat-treated at 150°C for 2 h under a nitrogen atmosphere according to the method for preparing carbon-sulfur composites in Example 1. The porous carbon with single-atom cobalt-O structure was mixed with elemental sulfur at a mass ratio of 1:1 to obtain a porous carbon-sulfur composite with single-atom cobalt-O structure (Co content 1.5 wt.%, O content 4 wt.%, sulfur content 50 wt.%, carbon content 45.5 wt.%).

[0030] Example 4:

[0031] Commercially available 20-micron diameter multi-arm carbon nanotubes were purchased. 1 g of the multi-arm carbon nanotubes were added to 10 ml of 68% nitric acid and refluxed at 150°C for 2 hours. After washing with water until neutral, the nanotubes were dried to obtain oxygen-containing carbon nanotubes. 0.1 g of the oxygen-containing carbon nanotubes were ultrasonically dispersed in 50 ml of ethanol, and 1 g of triphenylphosphine was added to dissolve it. Then, 10 ml of ethanol solution containing 10 mg of cobalt acetate was added. The mixture was stirred at room temperature for 3 hours, centrifuged, washed, and dried. After drying, the mixture was treated at 900°C for 2 hours under an argon atmosphere to obtain a porous carbon support with a single-atom cobalt-P structure. Following the method for preparing the carbon-sulfur composite in Example 1, porous carbon supported on single-atom cobalt-P and elemental sulfur were heat-treated at 150°C for 2 hours under a nitrogen atmosphere at a mass ratio of 1:1 to obtain a porous carbon-sulfur composite with single-atom cobalt-P (Co content 1.5 wt.%, P content 4.5 wt.%, sulfur content 50 wt.%, carbon content 44 wt.%).

[0032] Example 5:

[0033] Triphenylphosphine and phenolic resin were mixed at a mass ratio of 3:7 and heat-treated at 900°C under nitrogen protection for 2 hours to prepare phosphorus-doped carbon material. 0.1 g of the phosphorus-doped carbon material was ultrasonically dispersed in 50 ml of ethanol, and 10 ml of tetrahydrofuran solution containing 10 mg of ferric chloride was added. The mixture was stirred at room temperature for 3 hours, centrifuged, washed, dried, and then heat-treated at 900°C under argon atmosphere for 2 hours to obtain a porous carbon support with a single-atom iron-P structure. Following the method for preparing the carbon-sulfur composite in Example 1, porous carbon supported on single-atom iron-P and elemental sulfur were heat-treated at 150°C for 2 hours under nitrogen atmosphere at a mass ratio of 1:1 to obtain a composite of porous carbon and sulfur with single-atom iron-P (Fe content 1.2 wt.%, P content 2.8 wt.%, sulfur content 46 wt.%, carbon content 50 wt.%).

Claims

1. A sulfur cathode material composed of a metal atom M and a non-metal element N porous material, characterized in that: In composite sulfur cathode materials, the mass percentage of metal atoms M ranges from 0.1 wt.% to 10 wt.%. The nonmetallic element N is one or more of N, O, and P; its mass content is 0.5 wt.% to 10 wt.%. The sulfur-based material has a mass percentage content of 40 wt.% to 70 wt.%. The rest are porous materials; Non-metallic atoms are doped into the molecular framework structure of porous materials, and metal atoms are bonded to non-metallic atoms through coordination. Sulfur-based materials fill the pore structure of porous materials and are in contact with the MN structure. The porous materials have pore sizes of 2-100 nm and pore volumes of 0.5-5 cm³. 3 / g; The sulfur-based material in the composite sulfur cathode is one or more of elemental sulfur, sulfur-containing polymers, and polysulfide carbines, wherein the sulfur content is 20% to 90%, and the sulfur-containing polymer is one or more of sulfurized polyacrylonitrile and sulfurized polyaniline; The porous material is one or more of hollow mesoporous carbon spheres, carbon nanotubes, and porous carbon. The specific preparation method is as follows: (1) Using small molecules of non-metallic element N as a precursor, the precursor is one or two of triphenylphosphine, glucose, dopamine, phytic acid and a mixture of phenolic resin, wherein the small molecule precursor accounts for 10% to 50% of the weight of the mixture, and carbonization is carried out at 700℃ to 900℃ for 2h under nitrogen and / or argon protection to prepare porous carbon materials containing non-metallic elements; or carbon materials are treated with a mixed gas of argon / ammonia volume ratio of 1 to 3:1 at 500℃ to 600℃ for 2h; or carbon materials are refluxed at 80℃ to 150℃ for 2 to 4h with a mass ratio of 12mol / L concentrated nitric acid to carbon materials of 5 to 10:

1. (2) The salt containing metal element M is mixed with the prepared porous carbon material containing non-metal element at a mass ratio of 1:6 to 20 and ball-milled at 300 to 400 rpm for 4 to 6 hours. (3) The above mixture is heat-treated at 700℃~900℃ for 2h~4h under an inert atmosphere; (4) The prepared material is mixed with sulfur-based material at a mass ratio of 1:1 to 3 and then heat-treated in an argon atmosphere at 155℃ for 10h and 300℃ for 2h to prepare a sulfur cathode material composed of metal atom M-nonmetal element N porous material.

2. The sulfur cathode material according to claim 1, characterized in that: In composite sulfur cathode materials, the mass percentage of metal atoms M is 1 wt.% to 5 wt.%. The nonmetallic element N is one or more of N, O, and P; its mass content is 2 wt.% to 5 wt.%; The sulfur-based material has a mass percentage content of 50 wt.% to 65 wt.%.

3. The sulfur cathode material according to claim 1, characterized in that: The particle size of metal atom M is 0.01nm-0.05nm.

4. The sulfur cathode material according to claim 1, characterized in that: Metal atoms M include one or more of Fe, Co, Cu, and Ni.

5. The sulfur cathode material according to claim 1, characterized in that: The porous material is one or more of hollow mesoporous carbon spheres, carbon nanotubes, and porous carbon; the specific surface area of ​​the carbon material is 50–2000 m². 2 / g, pore size 20–50 nm, pore volume 3–4 cm³ 3 / g.

6. The sulfur cathode material according to claim 1, characterized in that: The sulfur content is 30% to 60%.

7. A method for preparing the sulfur cathode material according to any one of claims 1-4, characterized in that: (1) Using a small molecule containing the non-metallic element N as described in claim 1 as a precursor, wherein the precursor is one or two of triphenylphosphine, glucose, dopamine, phytic acid and a mixture of phenolic resin, wherein the small molecule precursor accounts for 10% to 50% of the mixture by weight, and carbonization is carried out at 700°C to 900°C for 2 hours under nitrogen and / or argon protection to prepare a porous carbon material containing the non-metallic element; or using a mixed gas with an argon / ammonia volume ratio of 1 to 3:1 at 500°C to 600°C for 2 hours; or carbon material refluxed at 80°C to 150°C for 2 to 4 hours with a mass ratio of 12 mol / L concentrated nitric acid to carbon material of 5 to 10:

1. (2) The salt containing metal element M is mixed with the prepared porous carbon material containing non-metal element at a mass ratio of 1:6 to 20 and ball-milled at 300 to 400 rpm for 4 to 6 hours. (3) The above mixture is heat-treated at 700℃~900℃ for 2h~4h under an inert atmosphere; (4) The prepared material is mixed with sulfur-based material at a mass ratio of 1:1 to 3 and then heat-treated in an argon atmosphere at 155℃ for 10h and 300℃ for 2h to prepare a sulfur cathode material composed of metal atom M-nonmetal element N porous material.

8. The application of the sulfur cathode material according to any one of claims 1-6 in a lithium-sulfur battery.

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