A method for preparing and applying a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries

Abstract

This invention discloses a method for preparing and applying a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries. It belongs to the field of materials preparation and application, specifically relating to a method for preparing and applying a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries. The purpose of this invention is to solve the defects of existing sulfur cathodes, such as poor conductivity, polysulfide dissolution and shuttle during charge and discharge, and high volume deformation of the electrode. These defects make the surface active material of the sulfur cathode in lithium-sulfur batteries and room-temperature sodium-sulfur batteries prone to pulverization and the overall electrode structure prone to collapse, resulting in poor battery capacity and cycle stability, which seriously affects the application of lithium-sulfur batteries and room-temperature sodium-sulfur batteries. The preparation method includes: 1. Preparing a silicon sphere close-packed material; 2. Preparing a honeycomb carbon mesh material; 3. Preparing a vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material; 4. Preparing a high-performance sulfur cathode composite material. This material is used as a cathode material for lithium-sulfur batteries or sodium-sulfur batteries.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and application, specifically relating to a method for preparing and applying a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries. Background Technology

[0002] With the rapid development of emerging fields such as electric vehicles, higher demands are being placed on the energy density of portable energy sources. Lithium-sulfur batteries, using lithium as the negative electrode, boast an energy density as high as 2600 Wh / kg. -1 Lithium-sulfur batteries are a very promising battery system. However, the limited global reserves of lithium resources cannot meet the huge energy market demand, leading to a continuous rise in lithium battery prices, which will inevitably affect the expansion of lithium batteries into the field of large-scale energy storage. Room temperature sodium-sulfur batteries have similar electrochemical principles to lithium-sulfur batteries, and also have the advantages of abundant and relatively inexpensive electrode materials, making them a promising battery system for large-scale energy storage applications.

[0003] Sulfur cathodes possess a theoretical specific capacity of 1675 mAh / g. Elemental sulfur is abundant, environmentally friendly, non-toxic, and inexpensive, making it a promising battery cathode material. However, sulfur cathodes suffer from poor conductivity, polysulfide dissolution and shuttle during charge and discharge, and high volumetric deformation of the electrode. These defects make the surface active material of sulfur cathodes in lithium-sulfur and room-temperature sodium-sulfur batteries prone to pulverization and the overall electrode structure susceptible to collapse, resulting in poor battery capacity and cycle stability, severely impacting the application of lithium-sulfur and room-temperature sodium-sulfur batteries. Therefore, the quality of sulfur cathode materials directly affects battery capacity, efficiency, and cycle performance, making it one of the key technologies for lithium-sulfur and room-temperature sodium-sulfur batteries. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing sulfur cathodes, such as poor conductivity, polysulfide dissolution and shuttle during charging and discharging, and high volume deformation of the electrode. These defects make the surface active material of the sulfur cathode in lithium-sulfur batteries and room-temperature sodium-sulfur batteries prone to pulverization and the overall electrode structure prone to collapse, resulting in poor battery capacity and cycle stability, which seriously affects the application of lithium-sulfur batteries and room-temperature sodium-sulfur batteries. The invention provides a method for preparing and applying a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries.

[0005] This invention provides a method for preparing a sulfur cathode composite material suitable for lithium-sulfur batteries and room-temperature sodium-sulfur batteries. The vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material prepared by this method can effectively improve the conductivity of the sulfur cathode in the battery, enhance the storage and utilization rate of sulfur in the electrode, and suppress the dissolution and shuttle of polysulfides in the electrolyte, suppress the volume change of the sulfur cathode during the charge and discharge process, improve the sulfur cycle efficiency during the charge and discharge process, and improve the performance and service life of sodium-sulfur batteries.

[0006] A method for preparing a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries is specifically carried out according to the following steps:

[0007] I. Preparation of close-packed silicon sphere materials:

[0008] ① Mix nano-spherical silicon with a liquid solvent in a certain proportion, stir vigorously and sonicate to form a suspension, and let it stand for several days;

[0009] ② The suspended liquid after standing is vacuum filtered, and then allowed to stand and dry to obtain silicon sphere close-packed material;

[0010] II. Preparation of honeycomb carbon mesh materials:

[0011] ① The silicon sphere close-packed material is immersed in a composite solution composed of solvent, resin and nonionic surfactant, left to stand for a period of time, and then dried to obtain powder material;

[0012] ② Under an inert atmosphere, the powder material is heated to the first calcination temperature, then calcined at the first calcination temperature for a period of time, and then heated to the second calcination temperature and carbonized at the second calcination temperature for a period of time to obtain a black powder material; the black powder material is cleaned to obtain a honeycomb carbon mesh material.

[0013] III. Preparation of vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite materials:

[0014] ① Mix titanate, inorganic acid, alcohol, soluble vanadium salt, soluble nitrogen source and activated carbon nanotubes evenly to obtain a mixed solution;

[0015] ② The honeycomb carbon mesh material obtained in step 2 is immersed in the mixed solution obtained in step 3①, magnetically stirred, then left to stand for a period of time, dried, and calcined to obtain a vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material.

[0016] IV. Preparation of high-performance sulfur cathode composite materials:

[0017] Sulfur powder was dissolved in CS2 to form a homogeneous solution. This solution was then added dropwise to a vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material. After standing for a period of time, a powder material was obtained. The powder material was placed in an N2 atmosphere, heated at a constant temperature, and then naturally cooled to room temperature to obtain a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries.

[0018] A ternary composite sulfur cathode material for lithium / sodium-sulfur batteries is used as the cathode material for lithium-sulfur batteries or sodium-sulfur batteries.

[0019] The principle of this invention:

[0020] Compared with other sulfur cathode composite materials, the vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon network / carbon nanotube ternary composite material prepared in this invention has a novel three-dimensional honeycomb cross-linked structure. The three-dimensional honeycomb carbon network and cross-linked carbon nanotubes can significantly improve the conductivity of the sulfur cathode, increase the electrochemical reaction sites, shorten the ion diffusion path, improve the discharge capacity of the sulfur cathode, and improve the rate performance of the sulfur cathode. The outer cross-linked carbon nanotubes, the middle honeycomb carbon network, and the embedded vanadium-nitrogen co-doped titanium dioxide particles inhibit the dissolution and shuttle of polysulfides in the electrolyte during charging and discharging through the synergistic effects of vanadium-nitrogen doping, physical encapsulation, physical adsorption, and chemical adsorption. At the same time, the internal pores and external encapsulation alleviate the volume expansion of the sulfur cathode during charging and discharging, which can enhance the electrochemical stability and cycle performance of the sulfur cathode. In summary, it significantly improves the performance and application scenarios of lithium-sulfur batteries and room-temperature sodium-sulfur batteries.

[0021] Advantages of this invention:

[0022] I. Compared with existing materials, the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared by this invention can leverage the synergistic effects of carbon material conductivity and physical adsorption, vanadium nitrogen doping modification, and titanium dioxide chemical adsorption to enhance the electrochemical energy storage characteristics of the sulfur cathode.

[0023] Second, compared with the prior art, the preparation process of the present invention is controllable, the production cost is low, and it can also be applied to the preparation and production of other carbon-metal oxide-sulfur cathode composite materials;

[0024] Third, the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared by this invention can achieve an initial discharge specific capacity of over 1480 mAh / g and over 1030 mAh / g in lithium-sulfur batteries and sodium-sulfur batteries, respectively. After 200 cycles, the discharge capacity can be maintained at over 745 mAh / g and over 600 mAh / g, respectively, and the coulombic efficiency can be stabilized at over 99%.

[0025] This invention provides a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries, suitable for use as the cathode in lithium-sulfur batteries and room-temperature sodium-sulfur batteries. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1;

[0027] Figure 2 Transmission electron microscope image of the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1;

[0028] Figure 3 The elemental distribution diagram is shown for the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1.

[0029] Figure 4The cycling performance of the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1 in lithium-sulfur batteries;

[0030] Figure 5 The cycling performance of the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1 in a room temperature sodium-sulfur battery. Detailed Implementation

[0031] Specific Implementation Method 1: This implementation method provides a preparation method for a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries, which is specifically completed according to the following steps:

[0032] I. Preparation of close-packed silicon sphere materials:

[0033] ① Mix nano-spherical silicon with a liquid solvent in a certain proportion, stir vigorously and sonicate to form a suspension, and let it stand for several days;

[0034] ② The suspended liquid after standing is vacuum filtered, and then allowed to stand and dry to obtain silicon sphere close-packed material;

[0035] II. Preparation of honeycomb carbon mesh materials:

[0036] ① The silicon sphere close-packed material is immersed in a composite solution composed of solvent, resin and nonionic surfactant, left to stand for a period of time, and then dried to obtain powder material;

[0037] ② Under an inert atmosphere, the powder material is heated to the first calcination temperature, then calcined at the first calcination temperature for a period of time, and then heated to the second calcination temperature and carbonized at the second calcination temperature for a period of time to obtain a black powder material; the black powder material is cleaned to obtain a honeycomb carbon mesh material.

[0038] III. Preparation of vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite materials:

[0039] ① Mix titanate, inorganic acid, alcohol, soluble vanadium salt, soluble nitrogen source and activated carbon nanotubes evenly to obtain a mixed solution;

[0040] ② The honeycomb carbon mesh material obtained in step 2 is immersed in the mixed solution obtained in step 3①, magnetically stirred, then left to stand for a period of time, dried, and calcined to obtain a vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material.

[0041] IV. Preparation of high-performance sulfur cathode composite materials:

[0042] Sulfur powder was dissolved in CS2 to form a homogeneous solution. This solution was then added dropwise to a vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material. After standing for a period of time, a powder material was obtained. The powder material was placed in an N2 atmosphere, heated at a constant temperature, and then naturally cooled to room temperature to obtain a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries.

[0043] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in the following ways: The liquid solvent mentioned in step one ① is one or more of anhydrous ethanol, water, n-butanol, acetone, chloroform, and carbon tetrachloride; the volume ratio of the nano-spherical silicon to the liquid solvent mentioned in step one ① is 1:(5-20); the stirring speed mentioned in step one ① is 500 r / min to 1500 r / min, and the stirring time is 30 min to 60 min; the ultrasonication time mentioned in step one ① is 30 min to 60 min; the standing time mentioned in step one ① is 1 day to 60 days. Other steps are the same as in Specific Implementation Method One.

[0044] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the vacuum degree of vacuum filtration in step one ② is 2000Pa to 4000Pa, and the vacuum filtration time is 4h to 8h. Other steps are the same as in Specific Implementation Method One or Two.

[0045] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in the following ways: The solvent in the composite solution described in step two① is one or more of ethanol, water, n-butanol, acetone, chloroform, and carbon tetrachloride; the resin is one or more of water-soluble phenolic resin, water-soluble acrylic resin, water-soluble amino resin, and water-soluble polyurethane resin; the nonionic surfactant is one or more of P123, fatty acid glycerides, fatty acid sorbitan, and polysorbate; the mass ratio of solvent, resin, and nonionic surfactant in the composite solution described in step two① is (6-10):(1-3):(0.5-1.5); the standing time described in step two① is 5-6 hours; the drying time is 12-36 hours at 100°C. Other steps are the same as in Specific Implementation Methods One to Three.

[0046] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in the following ways: In step two ②, the first calcination temperature is 300℃~450℃, and the calcination time is 2h~6h; in step two ②, the second calcination temperature is 800℃~1150℃, and the carbonization time is 1h~4h; in step two ②, the heating rate is 1℃ / min~5℃ / min; in step two ②, the black powder material is immersed in 20% hydrofluoric acid for 4h~6h, then removed and cleaned once, repeated 3 to 5 times to obtain the honeycomb carbon mesh material. Other steps are the same as in Specific Implementation Methods One to Four.

[0047] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in the following ways: The titanate esters mentioned in step three① are one or more of tetraisopropyl titanate, tetrabutyl titanate, tetraisopropyl di(dilauryl phosphite) titanate, and isopropyl tri(dioctyl pyrophosphoyloxy) titanate; the inorganic acid mentioned in step three① is one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; the alcohol mentioned in step three① is one or more of methanol, anhydrous ethanol, and n-butanol; the soluble vanadium salt mentioned in step three① is one or more of ammonium metavanadate, vanadium oxysulfate, and vanadium oxalate; the soluble nitrogen source mentioned in step three① is one or more of ammonia, urea, and ammonium nitrate. The other steps are the same as in Specific Implementation Methods One to Five.

[0048] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the preparation method of activated carbon nanotubes described in step three① is as follows:

[0049] Carbon nanotubes are placed in a mixed solution of H2SO4 and HNO3, sonicated at 70°C for 1 hour, then repeatedly centrifuged and washed with deionized water until the solution pH=7, and finally dried at 60°C for 10 hours to obtain activated carbon nanotubes. The volume ratio of H2SO4 to HNO3 in the mixed solution is 3:1, with H2SO4 having a mass fraction of 98% and HNO3 having a mass fraction of 65%. The mass ratio of titanate esters, inorganic acids, alcohols, soluble vanadium salts, soluble nitrogen sources, and activated carbon nanotubes in step three① is (0.5~1.5):(2~4):(4.5~6.5):(0.2~0.3):(0.1~0.3):(0.03~0.07). Other steps are the same as in specific embodiments one to six.

[0050] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in the following ways: the mass ratio of the honeycomb carbon mesh material to the mixed solution in step 3.② is 1:(40-60); the magnetic stirring speed in step 3.② is 500 r / min to 1500 r / min, and the magnetic stirring time is 2 h to 4 h; the settling time in step 3.② is 2 days; the drying in step 3.② is drying at 100℃ for 12 h to 36 h; the calcination atmosphere in step 3.② is an inert atmosphere, specifically nitrogen or argon; the calcination temperature is 300℃ to 500℃, and the calcination time is 1 h to 6 h. Other steps are the same as in Specific Implementation Methods One to Seven.

[0051] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in the following ways: the mass ratio of sulfur powder to CS2 in step four is (0.5–2.5):1; the mass ratio of sulfur powder to vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material in step four is 1:1; the settling time in step four is 0.5–6 hours; the constant temperature heating in step four is 150–160°C, and the constant temperature heating time is 8–10 hours. Other steps are the same as in Specific Implementation Methods One to Eight.

[0052] Specific Implementation Method 10: This implementation method is a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries used as the cathode material for lithium-sulfur batteries or sodium-sulfur batteries.

[0053] The beneficial effects of the present invention are verified using the following embodiments:

[0054] Example 1: A method for preparing a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries, specifically comprising the following steps:

[0055] I. Preparation of close-packed silicon sphere materials:

[0056] ① Mix nano-spherical silicon with liquid solvent in a certain proportion, stir at a stirring speed of 1000 r / min for 30 min; then sonicate for 30 min to form a suspension, and let it stand for 5 days;

[0057] The liquid solvent mentioned in step 1① is a mixture of anhydrous ethanol and water in a volume ratio of 3:1;

[0058] The volume ratio of the nano-spherical silicon to the liquid solvent mentioned in step 1① is 1:10;

[0059] ② The suspended liquid after standing is vacuum filtered, and then allowed to stand and dry to obtain silicon sphere close-packed material;

[0060] The vacuum degree of vacuum filtration described in step 1② is 2500Pa, and the vacuum filtration time is 4h.

[0061] II. Preparation of honeycomb carbon mesh materials:

[0062] ① The silicon sphere close-packed material is immersed in a composite solution composed of solvent, resin and nonionic surfactant, left to stand for 6 hours, and then dried at 100℃ for 12 hours to obtain powder material;

[0063] The solvent in the composite solution described in step 2① is anhydrous ethanol; the resin is type 431 water-soluble phenolic resin; and the nonionic surfactant is P123.

[0064] In step 2①, the mass ratio of solvent, resin, and nonionic surfactant in the composite solution is 8:2:1.

[0065] ② Under an inert atmosphere, the powder material is heated to 350℃ at a heating rate of 1℃ / min, then calcined at 350℃ for 4 hours, then heated to 900℃ at a heating rate of 5℃ / min, and carbonized at 900℃ for 2 hours to obtain a black powder material; the black powder material is cleaned to obtain a honeycomb carbon mesh material.

[0066] In step 2②, the black powder material is immersed in 20% hydrofluoric acid for 5 hours, then removed and cleaned once. This cleaning process is repeated 3 times to obtain the honeycomb carbon mesh material.

[0067] III. Preparation of vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite materials:

[0068] ① Mix titanate, inorganic acid, alcohol, soluble vanadium salt, soluble nitrogen source and activated carbon nanotubes evenly to obtain a mixed solution;

[0069] The titanate substance mentioned in step 3① is tetraisopropyl titanate;

[0070] The inorganic acid mentioned in step 3① is hydrochloric acid with a mass fraction of 37%;

[0071] The alcohol mentioned in step 3① is anhydrous ethanol;

[0072] The soluble vanadium salt mentioned in step 3① is ammonium metavanadate;

[0073] The soluble nitrogen source mentioned in step 3① is ammonia water with a mass fraction of 35%;

[0074] The mass ratio of titanate esters, inorganic acids, alcohols, soluble vanadium salts, soluble nitrogen sources, and activated carbon nanotubes mentioned in step 3① is 1:3:5.5:0.25:0.2:0.05;

[0075] The preparation method of activated carbon nanotubes described in step 3① is as follows:

[0076] Carbon nanotubes were placed in a mixed solution of H2SO4 and HNO3, sonicated at 70°C for 1 hour, then repeatedly centrifuged and washed with deionized water until the solution pH=7, and finally dried at 60°C for 10 hours to obtain activated carbon nanotubes. The volume ratio of H2SO4 to HNO3 in the mixed solution of H2SO4 and HNO3 was 3:1, wherein the mass fraction of H2SO4 was 98% and the mass fraction of HNO3 was 65%.

[0077] ② The honeycomb carbon mesh material obtained in step 2 is immersed in the mixed solution obtained in step 3①, magnetically stirred at 1000 r / min for 3 h, then left to stand for 2 days, dried at 100℃ for 12 h, and calcined to obtain a vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material.

[0078] The mass ratio of the honeycomb carbon mesh material to the mixed solution in step 3② is 1:50;

[0079] The calcination atmosphere described in step 3② is an inert atmosphere, specifically nitrogen; the calcination temperature is 450℃, and the calcination time is 4 hours.

[0080] IV. Preparation of high-performance sulfur cathode composite materials:

[0081] Sulfur powder was dissolved in CS2 to form a homogeneous solution. This solution was then added dropwise to a vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material. After standing for 0.5 h, the powder material was obtained. The powder material was placed in a N2 atmosphere and kept at 155 °C for 10 h. After naturally cooling to room temperature, a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries was obtained.

[0082] The mass ratio of sulfur powder to CS2 mentioned in step four is 0.5:1;

[0083] The mass ratio of sulfur powder to the vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon mesh / carbon nanotube ternary composite material in step four is 1:1.

[0084] Figure 1 This is a scanning electron microscope image of the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1;

[0085] from Figure 1 It can be seen that the basic structure of the ternary composite material prepared in Example 1 is honeycomb, and the basic lattice size of the honeycomb carbon network is about 200 nanometers. Vanadium and nitrogen-doped titanium dioxide particles are filled inside or between the honeycomb carbon network. The carbon nanotubes are three-dimensionally cross-linked in the composite material, which can not only prevent the micro-agglomeration of powder materials and increase the specific surface area, but also increase the conductivity and flexibility of the material. No large sulfur particles were found in the composite material. The sulfur dissolved in CS2 has entered the pores or voids of the material with the penetration of CS2.

[0086] Figure 2 Transmission electron microscope image of the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1;

[0087] from Figure 2 It is known that in the ternary composite material prepared in Example 1, the honeycomb carbon mesh has a hollow structure with a basic mesh size of about 200 nanometers; the carbon nanotubes have a diameter of 20-50 nanometers and are three-dimensionally cross-linked in the composite material; vanadium-nitrogen-doped titanium dioxide particles fill the inside or between the honeycomb carbon mesh, with a particle size of about 50 nanometers; no large sulfur particles were found in the composite material; in the special structure of the composite material prepared in Example 1, the three-dimensional cross-linking of the hollow honeycomb carbon mesh and carbon nanotubes can enhance the conductivity of the material, increase the specific surface area and porosity of the material, increase the electrochemical reaction active sites of sulfur, and inhibit the volume change of the sulfur cathode during charging and discharging; the vanadium-nitrogen-doped titanium dioxide particles can improve the chemical adsorption performance of the material for polysulfides, and work synergistically with the physical adsorption performance of the honeycomb carbon mesh and carbon nanotubes for polysulfides to inhibit the dissolution and shuttle of polysulfides in the electrolyte, thereby effectively improving the electrochemical performance of the sulfur cathode.

[0088] Figure 3 The elemental distribution diagram is shown for the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1.

[0089] from Figure 3 It can be seen that C, Ti, and S are distributed relatively uniformly in the composite material without obvious agglomeration. This indicates that the honeycomb carbon network, carbon nanotubes, vanadium-nitrogen-doped titanium dioxide, and sulfur in the composite material can all achieve uniform loading without particle agglomeration, which is beneficial to the electrochemical performance.

[0090] Example 2: Using the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1 as the cathode, the lithium-sulfur battery was prepared according to the following steps:

[0091] Using a general method, with nickel foam / carbon cloth / copper foil as the current collector, powder samples (ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1), conductive agent acetylene black, and binder (polyvinylidene fluoride) were mixed in a mass ratio of 8:1:1. An appropriate amount of N-methyl dipyrrolidone was added as a solvent. After grinding in an agate mortar for half an hour, a uniform slurry was formed. The slurry was evenly coated onto discs of nickel foam / carbon cloth / copper foil with a brush. After vacuum drying at 80-100℃ for 10 hours, the electrode sheets were formed by pressing them into sheets at 10-25 MPa using a powder press. The formed electrode sheets were used as working electrodes, lithium metal sheets as counter electrodes and reference electrodes, polypropylene porous membranes (Celgard 2400) as separators, and lithium-sulfur battery-specific electrolytes as electrolytes. The CR2025 / CR2032 button batteries were assembled in an argon-atmosphere glove box.

[0092] Figure 4 The cycling performance of the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1 in lithium-sulfur batteries;

[0093] from Figure 4 It can be seen that after the SEI film is stably formed in the first week, the reversible discharge capacity of the prepared composite sulfur cathode material in the lithium sulfur battery is 1050 mAh / g; after 50 cycles, the charge and discharge capacity of the sulfur cathode begins to stabilize, with coulombic efficiency above 99.5%; after 200 cycles, the discharge capacity of the prepared composite sulfur cathode is 770 mAh / g, the capacity retention rate is 73.3%, and the average capacity loss per week is 1.4 mAh / g.

[0094] Example 3: Using the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1 as the cathode, a room-temperature sodium-sulfur battery was prepared according to the following steps:

[0095] Using a general method, with nickel foam / carbon cloth / copper foil as the current collector, powder samples, conductive agent acetylene black, and binder (polyvinylidene fluoride) were mixed in a mass ratio of 8:1:1. An appropriate amount of N-methyldipyrrolidone was added as a solvent, and the mixture was ground in an agate mortar for half an hour to form a uniform slurry. The slurry was evenly applied to discs of nickel foam / carbon cloth / copper foil using a brush. After vacuum drying at 80-100℃ for 10 hours, the slurry was pressed into electrode sheets using a powder press at 10-25 MPa. The prepared electrode sheets were used as the working electrodes, sodium metal sheets as the counter and reference electrodes, and a polypropylene porous membrane (Celgard 2400) as the separator. The electrolyte was a sodium-sulfur battery-specific electrolyte. The CR2025 / CR2032 button batteries were assembled in an argon-atmosphere glove box.

[0096] Figure 5 Cycling performance of the ternary composite sulfur cathode material for lithium / sodium-sulfur batteries prepared in Example 1 in a room temperature sodium-sulfur battery;

[0097] from Figure 5 It can be seen that after the SEI film is stably formed in the first week, the reversible discharge capacity of the prepared composite sulfur cathode material in the lithium sulfur battery is 890 mAh / g; after 100 cycles, the charge and discharge capacity of the sulfur cathode begins to stabilize, with coulombic efficiency above 98.5%; after 200 cycles, the discharge capacity of the prepared composite sulfur cathode is 620 mAh / g, the capacity retention rate is 69.6%, and the average capacity loss per week is 1.4 mAh / g.

Claims

1. A method for preparing a ternary composite sulfur cathode material for lithium / sodium sulfur batteries, characterized in that The preparation method is specifically completed according to the following steps: I. Preparation of the silicon sphere dense packing body material:

1. Mix the nanometer spherical silicon and the liquid solvent according to a certain proportion, form a suspension after intense stirring and ultrasonic treatment, and stand for several days; 2. Vacuum filter the suspension after standing, and then stand and dry to obtain the silicon sphere dense packing body material; II. Preparation of the honeycomb carbon net material:

1. Immerse the silicon sphere dense packing body material into a composite solution composed of a solvent, a resin and a non-ionic surfactant, stand for a period of time, and then dry to obtain the powder material; 2. Under an inert atmosphere, heat the powder material to a first calcination temperature, calcine at the first calcination temperature for a period of time, then heat to a second calcination temperature, carbonize at the second calcination temperature for a period of time, and obtain the black powder material; wash the black powder material to obtain the honeycomb carbon net material; III. Preparation of the vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon net / carbon nanotube ternary composite material:

1. Mix the titanate, inorganic acid, alcohol, soluble vanadium salt, soluble nitrogen source and activated carbon nanotube uniformly to obtain a mixed solution; 2. Immerse the honeycomb carbon net material obtained in step II into the mixed solution obtained in step III 1, magnetically stir, stand for a period of time, dry, and calcine to obtain the vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon net / carbon nanotube ternary composite material; IV. Preparation of the high-performance sulfur positive electrode composite material: Dissolve sulfur powder in CS2 to form a uniform solution, then add the solution into the vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon net / carbon nanotube ternary composite material in batches, stand for a period of time, and obtain the powder material; place the powder material in a N2 atmosphere, heat at a constant temperature, and naturally cool to room temperature to obtain the ternary composite sulfur positive electrode material for lithium / sodium sulfur batteries.

2. The preparation method of the ternary composite sulfur cathode material for lithium / sodium sulfur batteries according to claim 1, characterized in that The liquid solvent in step I 1 is one or more of anhydrous ethanol, water, n-butanol, acetone, chloroform and carbon tetrachloride; the volume ratio of the nanometer spherical silicon to the liquid solvent in step I 1 is 1:(5-20); the stirring speed of the intense stirring in step I 1 is 500-1500 r / min, and the time of the intense stirring is 30-60 min; the time of the ultrasonic treatment in step I 1 is 30-60 min; and the standing time in step I 1 is 1-60 days.

3. The method for preparing a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries according to claim 1, characterized in that... The vacuum degree of the vacuum filtration in step I 2 is 2000-4000 Pa, and the time of the vacuum filtration is 4-8 h.

4. The method for preparing a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries according to claim 1, characterized in that... The solvent in the complex solution in step two 1 is one or more of ethanol, water, n-butanol, acetone, chloroform and carbon tetrachloride; the resin is one or more of water-soluble phenolic resin, water-soluble acrylic resin, water-soluble amino resin and water-soluble polyurethane resin; the non-ionic surfactant is one or more of P123, fatty acid glyceride, fatty acid sorbitan and polysorbate; the mass ratio of the solvent, the resin and the non-ionic surfactant in the complex solution in step two 1 is (6-10):(1-3):(0.5-1.5); the standing in step two 1 is standing for 5-6 hours; and the drying is drying at 100℃ for 12-36 hours.

5. The method for preparing a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries according to claim 1, characterized in that... The first calcination temperature in step two 2 is 300-450℃, and the calcination time is 2-6 hours; the second calcination temperature in step two 2 is 800-1150℃, and the carbonization time is 1-4 hours; the heating rate in step two 2 is 1-5℃ / min; the black powder material in step two 2 is immersed in 20% hydrofluoric acid for 4-6 hours, and after being taken out, one cleaning is completed, and the cleaning is repeated for 3-5 times to obtain the honeycomb carbon network material.

6. The method for preparing a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries according to claim 1, characterized in that... The titanate in step three 1 is one or more of tetraisopropyl titanate, butyl titanate, tetraisopropyl di(dilauryl phosphite) titanate and isopropyl tri(dioctyl pyrophosphato) titanate; the inorganic acid in step three 1 is one or more of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid; the alcohol in step three 1 is one or more of methanol, anhydrous ethanol and n-butanol; the soluble vanadium salt in step three 1 is one or more of ammonium metavanadate, vanadyl sulfate and oxalate; and the soluble nitrogen source in step three 1 is one or more of ammonia, urea and ammonium nitrate.

7. The method according to claim 1, wherein the method is characterized by The preparation method of the activated carbon nanotube in step three 1 is as follows: The carbon nanotube is put into a mixed solution of H2SO4 and HNO3, ultrasonic treatment is carried out at 70℃ for 1 hour, repeated centrifugation and washing are carried out with deionized water until the pH of the solution is 7, and finally drying is carried out at 60℃ for 10 hours to obtain the activated carbon nanotube; the volume ratio of H2SO4 to HNO3 in the mixed solution of H2SO4 and HNO3 is 3:1, the mass fraction of H2SO4 is 98%, and the mass fraction of HNO3 is 65%; the mass ratio of the titanate, the inorganic acid, the alcohol, the soluble vanadium salt, the soluble nitrogen source and the activated carbon nanotube in step three 1 is (0.5-1.5):(2-4):(4.5-6.5):(0.2-0.3):(0.1-0.3):(0.03-0.07).

8. The method for preparing a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries according to claim 1, characterized in that... The mass ratio of the honeycomb carbon net material to the mixed solution in the step three 2 is 1:(40-60); the speed of the magnetic stirring in the step three 2 is 500r / min-1500r / min, the time of the magnetic stirring is 2h-4h; the time of the standing in the step three 2 is 2 days; the drying in the step three 2 is drying at 100℃ for 12h-36h; the atmosphere of the calcination in the step three 2 is inert atmosphere, the inert atmosphere is nitrogen or argon; the temperature of the calcination is 300℃-500℃, the time of the calcination is 1h-6h.

9. The method for preparing a ternary composite sulfur cathode material for lithium / sodium-sulfur batteries according to claim 1, characterized in that... The mass ratio of the sulfur powder to CS2 in the step four is (0.5-2.5):1; the mass ratio of the sulfur powder to the vanadium-nitrogen co-doped titanium dioxide / honeycomb carbon net / carbon nanotube ternary composite material in the step four is 1:1; the time of the standing in the step four is 0.5h-6h; the temperature of the constant temperature heating in the step four is 150℃-160℃, the time of the constant temperature heating in the step four is 8h-10h.

10. Use of a ternary composite sulfur cathode material for lithium / sodium sulfur batteries prepared by the method of claim 1, characterized in that The ternary composite sulfur positive electrode material for lithium / sodium sulfur battery is used as a positive electrode material of a lithium sulfur battery or a sodium sulfur battery.

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