Carbon-coated sulfur-titanium-niobium oxide composite positive electrode material, preparation method and application thereof

Abstract

The application discloses a carbon-coated sulfur-titanium-niobium oxide composite positive electrode material and a preparation method and application thereof, and belongs to the technical field of lithium metal battery materials. The application aims to solve the problem of poor rate performance caused by low ion conductivity and electronic conductivity of a sulfur positive electrode material. In the application, high-conductivity polar titanium-niobium oxide (TiNb2O7) is used as a carrier, and is combined with elemental sulfur through a solvent thermal sulfur storage method to obtain a sulfur-titanium-niobium oxide composite material. Meanwhile, in order to further improve the electronic conductivity of the composite material, a plasma technology is used to coat the surface of the composite material with carbon, so that the electronic conductivity of the composite material is significantly improved. The finally obtained carbon-coated sulfur-titanium-niobium oxide composite positive electrode material has high coulomb efficiency, excellent rate performance, and the cycle stability of the carbon-coated sulfur-titanium-niobium oxide composite positive electrode material is also significantly improved, and has a wide application prospect in the field of lithium metal batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium metal battery materials technology, specifically to a carbon-coated sulfur-titanium niobium oxide composite cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries possess excellent electrochemical performance and are widely used in electronic devices, transportation, and energy storage. However, limited by the theoretical specific capacity of the positive and negative electrode materials, the energy density of conventional lithium-ion batteries currently struggles to exceed 300 Wh / kg. To meet the technological demands of portable electronic devices and electric vehicles for lightweight design and long driving range, the development of high-energy-density rechargeable batteries is of paramount importance. Lithium-sulfur batteries have attracted considerable attention due to their high energy density and environmentally friendly characteristics.

[0003] Compared to traditional lithium-ion batteries, elemental sulfur, the positive electrode active material in lithium-sulfur batteries, is abundant on Earth and boasts advantages such as low cost and environmental friendliness. However, elemental sulfur and its oligomeric polysulfides (Li2S2 / Li2S) exhibit poor conductivity, leading to increased battery impedance and severe polarization, thereby reducing energy conversion efficiency and failing to meet high-rate charge-discharge requirements. Furthermore, during discharge, the sulfur cathode not only experiences volume expansion leading to electrode structure collapse but also generates a large amount of polysulfides, causing a "shuttle effect" and resulting in low charge-discharge efficiency. Consequently, lithium-sulfur batteries suffer from poor rate performance and cycle stability. To address this issue, strategies such as combining elemental sulfur with conductive carbon materials or metal oxides are commonly employed to modify the elemental sulfur cathode material. Typically, elemental sulfur is combined with metal oxides such as TiO2 and Fe2O3 to enhance the adsorption capacity for polysulfides, thereby improving the cycle stability of lithium-sulfur batteries. However, when metal oxide materials are combined with sulfur, the composite material does not provide reversible charge-discharge capacity within the operating voltage range of lithium-sulfur batteries, which leads to a decrease in the specific capacity of the composite material and is not conducive to improving the energy density of lithium-sulfur batteries.

[0004] Meanwhile, combining elemental sulfur with carbon materials can effectively improve the conductivity of elemental sulfur and suppress the volume expansion of sulfur during charging and discharging, as well as the shuttle effect during discharge. However, conventional sulfur-carbon composite materials are generally prepared through mechanical mixing or sulfur infiltration using carbon as a carrier. These methods typically require a higher carbon content (>30 wt.%) to improve the electronic conductivity of the cathode composite material and thus enhance the battery's rate performance. While increasing carbon content improves conductivity, carbon does not provide additional capacity; therefore, combining active sulfur with a large amount of carbon can reduce the energy density of lithium-sulfur batteries. Furthermore, the intermolecular bonds between nonpolar carbon and polar polysulfides are weak, failing to effectively address the polysulfide problem generated during sulfur cathode discharge. Summary of the Invention

[0005] To address the shortcomings of elemental sulfur cathode materials in terms of rate performance and cycle stability, this invention provides a carbon-coated sulfur-titanium niobium oxide composite cathode material, its preparation method, and its applications.

[0006] This invention utilizes highly conductive polar titanium niobium oxide as a carrier and employs a solvothermal sulfur storage method to composite it with elemental sulfur. This effectively improves the conductivity of elemental sulfur and suppresses the volume expansion of elemental sulfur and the polysulfide shuttle problem during discharge. To further enhance the electronic conductivity of the composite material, plasma technology is used to perform low-temperature and ultra-low-dose surface carbon coating treatment on the surface of the sulfur-titanium niobium oxide composite material. The resulting carbon-coated sulfur-titanium niobium oxide composite cathode material exhibits high ionic and electronic conductivity. Furthermore, the confinement of the polar titanium niobium oxide within the composite material and the physical barrier of the external carbon material confine polysulfides within the composite cathode material, and all chemical reactions occur on the surface of the highly conductive material. This provides an effective way to improve the charge-discharge efficiency and overall performance of the battery.

[0007] The specific technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] This invention provides a method for preparing a carbon-coated sulfur-titanium niobium oxide composite cathode material, comprising the following steps:

[0009] (1) The titanium precursor and the niobium precursor are uniformly mixed in an organic solvent at room temperature, additives are added, the mixture of the three is poured into the inner liner, and then the inner liner is placed in the reaction vessel for solvothermal reaction.

[0010] (2) The obtained precipitate was calcined to obtain titanium niobium oxide material;

[0011] (3) Elemental sulfur and titanium niobium oxide were uniformly mixed in an organic solvent at room temperature and poured into the inner liner of a reaction vessel for a solvothermal reaction. After the reaction, the mixture was filtered and dried to obtain a sulfur-titanium niobium oxide composite material.

[0012] (4) The benzene-based carbon source is sealed inside a glass container with a gas valve. The sulfur-titanium niobium oxide composite material obtained in step (3) is placed inside a plasma reactor and carbon material is coated on the surface of the sulfur-titanium niobium oxide composite material by plasma-enhanced chemical vapor deposition to obtain carbon-coated sulfur-titanium niobium oxide composite cathode material.

[0013] By employing the above technical solution, this invention uses highly conductive polar titanium niobium oxide (TiNb2O7) as a carrier and combines it with elemental sulfur via a solvothermal sulfur storage method to obtain a sulfur-titanium niobium oxide composite material. Simultaneously, to further improve the electronic conductivity of the composite material, plasma technology is used to coat the surface of the composite material with a low amount of carbon, significantly improving the electronic conductivity. The resulting carbon-coated sulfur-titanium niobium oxide composite cathode material not only exhibits high coulombic efficiency and excellent rate performance but also significantly improved cycle stability, showing broad application prospects in the field of lithium metal batteries.

[0014] The following are preferred technical solutions of the present invention:

[0015] Preferably, in step (1), the titanium precursor is at least one of tetrabutyl titanate, tetraethyl titanate, and titanium dioxide; the niobium precursor is at least one of niobium pentachloride, niobium oxalate, and niobium pentoxide; and the additive is at least one of polystyrene, polyvinyl alcohol, and polylactic acid.

[0016] Preferably, in step (1), the purity of the titanium precursor is ≥98% and the purity of the niobium precursor is ≥99%.

[0017] Preferably, in step (1), the molar ratio of titanium precursor to niobium precursor is 1:2.

[0018] Preferably, in step (1), the amount of additive is 3 to 5 wt.% of the total mass of the titanium precursor and the niobium precursor. More preferably, the purity of the additive is ≥96%.

[0019] Preferably, in step (1), the conditions for the solvothermal reaction are: the organic solvent is at least one of ethanol, ethylene glycol, isopropanol and butanol, the reaction temperature is 140-180℃, the reaction time is 8-20h, and the mass ratio of the liquid to the material is 1:4-1:8.

[0020] Preferably, in step (2), the precipitate is washed multiple times with deionized water and dried, and then calcined in a muffle furnace. More preferably, the drying conditions are drying at 60-120°C for 1-12 hours.

[0021] Preferably, in step (2), the calcination conditions are: calcination temperature of 700-900℃, calcination time of 5-10h, and heating rate of 2-5℃ / min.

[0022] Preferably, in step (2), the titanium niobium oxide material is TiNb2O7 with a specific surface area of ​​100–300 m². 2 / g, with pore size ranging from 1 to 50 nm and particle size ranging from 2 to 8 μm.

[0023] Preferably, in step (3), the mass ratio of elemental sulfur to titanium niobium oxide is 7:3 to 9:1.

[0024] Preferably, in step (3), the conditions for the solvothermal reaction are: the organic solvent is at least one of ethanol, ethylene glycol, isopropanol, butanol and carbon disulfide, the reaction temperature is 140-180℃, the reaction time is 12-24h, and the mass ratio of the liquid to the material is 1:4-1:8.

[0025] Preferably, in step (3), after the solvothermal reaction, the mixture is subjected to filtration and drying. More preferably, the drying conditions are drying at 60-100°C for 5-14 hours.

[0026] Preferably, in step (4), the carbon source of the benzene-based substance includes at least one of benzene, toluene, ethylbenzene, and xylene. Because benzene-based substances contain benzene rings and have unique conjugated double bonds, they are more likely to form highly conductive carbon materials during plasma reactions.

[0027] Preferably, in step (4), the reaction conditions for plasma-enhanced chemical vapor deposition include: vacuuming to a vacuum level of 10-30 Pa, heating temperature of 30-150 °C, radio frequency power of 100-500 W, and reaction time of 5-30 min.

[0028] Preferably, in step (4), the carbon content in the carbon-coated sulfur-titanium niobium oxide composite cathode material is 2-5 wt.%. More preferably, the thickness of the carbon coating on the surface of the sulfur-titanium niobium oxide composite material is 10-20 nm.

[0029] Preferably, in step (4), carbon material is coated onto the surface of the sulfur-titanium niobium oxide composite material by plasma-enhanced chemical vapor deposition, specifically including:

[0030] The sulfur-titanium niobium oxide composite material was placed inside the plasma generator cavity, and the air inside the cavity was evacuated. When the internal vacuum degree was 10-30 Pa, heating was started. When the muffle furnace was heated to 30-150℃, benzene-based carbon source gas molecules were introduced into the tube by volatilizing benzene-based substances. The radio frequency power was turned on and adjusted to 100-500W. The reaction time was 5-30 min. After the reaction was completed, heating was stopped, and the gas pressure inside the tube was backfilled to standard atmospheric pressure with argon. After the furnace cooled down, the carbon-coated sulfur-titanium niobium oxide composite cathode material was obtained.

[0031] A further preferred embodiment of the method for preparing a carbon-coated sulfur-titanium niobium oxide composite cathode material includes the following steps:

[0032] (1) Mix titanium precursor with purity ≥98% and niobium precursor with purity ≥99% uniformly in an organic solvent at room temperature, add 3-5 wt.% additive, stir magnetically for 15-20 min, pour the mixed solution into the inner liner of polytetrafluoroethylene, and then put the inner liner into the reaction vessel and carry out a solvothermal reaction at a certain temperature for several hours.

[0033] (2) After the reactor is cooled to room temperature, the inner liner of the reactor is opened. The precipitate is washed with deionized water 3 to 5 times and dried in a forced-air drying oven for several hours. Then the material is transferred to a muffle furnace and calcined at a certain temperature for several hours to obtain titanium niobium oxide material.

[0034] (3) Elemental sulfur and titanium niobium oxide were uniformly mixed in an organic solvent at room temperature and magnetically stirred for 10-15 minutes. The mixture was then poured into a reaction vessel with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at a certain temperature for several hours. After the reaction, the reaction vessel was opened, and the mixture was then filtered and dried for several hours to obtain a sulfur-titanium niobium oxide composite material.

[0035] (4) The benzene-based carbon precursor source is sealed inside a glass container with a gas valve. The sulfur-titanium niobium oxide composite material obtained in step (3) is placed inside the plasma generator cavity, and carbon material is coated on the surface of the sulfur-titanium niobium oxide composite material by plasma-enhanced chemical vapor deposition to obtain carbon-coated sulfur-titanium niobium oxide composite cathode material, wherein the sulfur element accounts for 67-88 wt.% of the total composite cathode material, the titanium niobium oxide accounts for 10-28 wt.% and the carbon element accounts for 2-5 wt.%.

[0036] In this invention, the porous polar material titanium niobium oxide, due to its excellent conductivity, enables rapid ion charging and discharging at high rates. This porous structure provides effective sulfur storage space for the composite of titanium niobium oxide and elemental sulfur, alleviating the problem of sulfur volume expansion during charging and discharging. Generally, when polar metal oxide materials such as TiO2 and Fe2O3 are combined with sulfur, although they can enhance the adsorption capacity for polysulfides and improve the cycle stability of lithium-sulfur batteries, they do not provide reversible charge-discharge capacity within the operating voltage range of lithium-sulfur batteries, leading to a decrease in the specific capacity of the composite material, which is detrimental to improving the energy density of lithium-sulfur batteries. However, titanium niobium oxide material has a high reversible specific capacity (387 mAh / g) in the 1V-3V voltage range. After being combined with sulfur, it not only achieves the adsorption of polysulfides by conventional metal oxide materials but also provides additional capacity within the operating voltage range of lithium-sulfur batteries. Therefore, it can improve the cycle stability of the sulfur cathode without significantly reducing the energy density of lithium-sulfur batteries.

[0037] The present invention also provides a carbon-coated sulfur-titanium niobium oxide composite cathode material prepared by any of the above preparation methods.

[0038] The present invention also provides an application of the carbon-coated sulfur-titanium niobium oxide composite cathode material prepared by any of the above preparation methods in the field of lithium metal batteries.

[0039] Based on the above technical solution, the present invention has the following beneficial effects:

[0040] (1) The titanium niobium oxide synthesized by the solvothermal method described in this invention is composed of microspheres with a particle size of 2 to 8 μm, which has a large specific surface area and a pore size distribution of less than 50 nm, providing a certain space for sulfur storage and alleviating the problem of volume expansion during elemental sulfur discharge.

[0041] (2) This invention effectively improves the conductivity of elemental sulfur by combining it with titanium niobium oxide. Simultaneously, this material exhibits stronger adsorption of polysulfides, enhancing the overall cycle stability of the material. Titanium niobium oxide itself possesses a high discharge specific capacity, and when combined with sulfur, it provides a certain capacity support within the operating voltage range of lithium-sulfur batteries without significantly reducing the battery's energy density.

[0042] (3) The present invention uses plasma technology to coat the surface of sulfur-titanium niobium oxide composite material with carbon material thickness of 10-20 nm, and has a low carbon content inside the composite cathode material, which can significantly improve the electronic conductivity of the composite material, improve the rate performance of lithium-sulfur battery and the charge and discharge efficiency of the battery, and has broad market application prospects.

[0043] (4) The present invention achieves carbon coating through plasma technology. The operation process is simple and efficient, and it is suitable for large-scale industrial production. Attached Figure Description

[0044] Figure 1 This is a SEM image of the titanium niobium oxide material in Example 1 of this invention;

[0045] Figure 2 These are BET diagrams of the titanium niobium oxide material before and after sulfur storage in Example 1 of this invention;

[0046] Figure 3 This is a pore volume and pore size distribution diagram of the titanium niobium oxide material in Embodiment 1 of the present invention;

[0047] Figure 4 This is a SEM image of the carbon-coated sulfur-titanium niobium oxide composite cathode material in Example 1 of this invention;

[0048] Figure 5 This is a comparison chart of the initial charge-discharge curves of the two materials in Example 1 and Comparative Example 1 of the present invention;

[0049] Figure 6This is a cycle capacity diagram of two materials in Embodiment 1 and Comparative Example 2 of the present invention at different expansion rates. Detailed Implementation

[0050] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0051] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, or instruments used in the embodiments, unless otherwise specified, can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention can all achieve the reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0052] Example 1

[0053] (1) Mix 0.945g tetrabutyl titanate (purity 98%), 1.5g niobium pentachloride (purity 99.9%) and 0.122g polyvinyl alcohol in ethanol solution at room temperature 25°C with a material-to-liquid mass ratio of 1:6. Stir magnetically for 20min. Pour the mixed solution into a polytetrafluoroethylene inner liner. Then place the inner liner into a high-pressure reactor and carry out a solvothermal reaction at 180°C for 14h.

[0054] (2) After the reactor cooled to room temperature, the inner liner of the reactor was opened. The obtained precipitate was washed three times with deionized water and dried in a 60°C forced-air drying oven for 12 hours. Then, the material was transferred to a muffle furnace and calcined at 850°C for 8 hours to obtain a particle size and pore size of 3-6 μm and 2-30 nm, respectively, with a specific surface area of ​​300 m². 2 / g of mesoporous titanium niobium oxide material;

[0055] (3) 0.8 g of elemental sulfur and 0.2 g of titanium niobium oxide were mixed in an ethanol solution at room temperature with a material-to-liquid mass ratio of 1:6. The mixture was magnetically stirred for 10 min and then poured into a high-pressure reactor with a polytetrafluoroethylene liner. The mixture was subjected to a solvothermal reaction at 160 °C for 16 h. After the reaction, the reactor was opened, and the mixture was then filtered and dried at 60 °C for 12 h to obtain a sulfur-titanium niobium oxide composite material.

[0056] (4) Toluene (containing 91.3% carbon) was sealed inside a glass container with a gas valve. The sulfur-titanium niobium oxide composite material obtained in step (3) was placed inside the plasma generator cavity. The vacuum pump was turned on to evacuate the plasma generator cavity to a vacuum of 10 Pa. The plasma generator was then turned on. When the temperature inside the cavity reached 100°C, the radio frequency power supply was turned on and the radio frequency power was adjusted to 350W. The reaction was carried out under these conditions for 10 minutes to obtain a carbon-coated sulfur-titanium niobium oxide composite cathode material, in which the sulfur element accounted for 77 wt.% of the total composite cathode material, the titanium niobium oxide accounted for 20 wt.%, and the carbon element accounted for 3 wt.%.

[0057] Example 2

[0058] (1) Mix 0.945g tetrabutyl titanate (purity 98%), 1.5g niobium pentachloride (purity 99.9%) and 0.098g polystyrene in ethylene glycol solution at room temperature 25°C with a material-to-liquid mass ratio of 1:4. Stir magnetically for 15min. Pour the mixed solution into a polytetrafluoroethylene inner liner. Then place the inner liner into a high-pressure reactor and carry out a solvothermal reaction at 160°C for 14h.

[0059] (2) After the reactor cooled to room temperature, the inner liner of the reactor was opened. The obtained precipitate was washed four times with deionized water and dried in an 80°C forced-air drying oven for 6 hours. Then, the material was transferred to a muffle furnace and calcined at 900°C for 6 hours to obtain a particle size and pore size of 4–5 μm and 5–44 nm, respectively, with a specific surface area of ​​174 m². 2 / g of mesoporous titanium niobium oxide material;

[0060] (3) 0.9 g of elemental sulfur and 0.1 g of titanium niobium oxide were mixed in ethylene glycol solution at room temperature with a material-to-liquid mass ratio of 1:4. The mixture was magnetically stirred for 15 min and then poured into a high-pressure reactor with a polytetrafluoroethylene liner. The mixture was subjected to a solvothermal reaction at 180 °C for 12 h. After the reaction, the reactor was opened, and the mixture was then filtered and dried at 80 °C for 10 h to obtain a sulfur-titanium niobium oxide composite material.

[0061] (4) Ethylbenzene (containing 90.6% carbon) was sealed inside a glass container with a gas valve. The sulfur-titanium niobium oxide composite material obtained in step (3) was placed inside the plasma generator cavity. The vacuum pump was turned on to evacuate the plasma generator cavity to a vacuum level of 30 Pa. Then the plasma generator was turned on. When the temperature inside the cavity reached 80°C, the radio frequency power supply was turned on and the radio frequency power was adjusted to 300W. The reaction was carried out under these conditions for 15 minutes to obtain a carbon-coated sulfur-titanium niobium oxide composite cathode material, in which the sulfur element accounted for 88 wt.% of the total composite cathode material, the titanium niobium oxide accounted for 10 wt.%, and the carbon element accounted for 2 wt.%.

[0062] Example 3

[0063] (1) 1.26g tetrabutyl titanate (purity 98%), 2g niobium pentachloride (purity 99.9%) and 0.098g polylactic acid were mixed in ethanol solution at room temperature 25°C with a material-to-liquid mass ratio of 1:8. The mixture was magnetically stirred for 20 min. The mixed solution was poured into a polytetrafluoroethylene inner liner and then placed in a high-pressure reactor. The reaction was carried out at 140°C for 20 h using a solvothermal method.

[0064] (2) After the reactor cooled to room temperature, the inner liner of the reactor was opened. The obtained precipitate was washed five times with deionized water and dried in a 120°C forced-air drying oven for 1 hour. Subsequently, the material was transferred to a muffle furnace and calcined at 750°C for 9 hours to obtain a particle size and pore size of 3–6 μm and 10–50 nm, respectively, with a specific surface area of ​​137 m². 2 / g of mesoporous titanium niobium oxide material;

[0065] (3) 0.8 g of elemental sulfur and 0.2 g of titanium niobium oxide were mixed in carbon disulfide solution at room temperature with a material-to-liquid mass ratio of 1:8. The mixture was magnetically stirred for 10 min and then poured into a high-pressure reactor with a polytetrafluoroethylene liner. The mixture was subjected to a solvothermal reaction at 140 °C for 20 h. After the reaction, the reactor was opened, and the mixture was then filtered and dried at 80 °C for 12 h to obtain a sulfur-titanium niobium oxide composite material.

[0066] (4) Ethylbenzene (containing 90.6% carbon) was sealed inside a glass container with a gas valve. The sulfur-titanium niobium oxide composite material obtained in step (3) was placed inside the plasma generator cavity. The vacuum pump was turned on to evacuate the plasma generator cavity to a vacuum level of 15 Pa. The plasma generator was then turned on. When the temperature inside the cavity reached 120°C, the radio frequency power supply was turned on and the radio frequency power was adjusted to 400W. The reaction was carried out under these conditions for 5 minutes to obtain a carbon-coated sulfur-titanium niobium oxide composite cathode material, in which the sulfur element accounted for 78 wt.% of the total composite cathode material, the titanium niobium oxide accounted for 20 wt.%, and the carbon element accounted for 2 wt.%.

[0067] Example 4

[0068] (1) Mix 0.424g tetraethyl titanate (purity 99%), 2g niobium oxalate (purity 99%) and 0.121g polyvinyl alcohol in butanol solution at room temperature 25°C with a material-to-liquid mass ratio of 1:4. Stir magnetically for 20 min, pour the mixed solution into a polytetrafluoroethylene inner liner, and then place the inner liner into a high-pressure reactor for a solvothermal reaction at 180°C for 8 h.

[0069] (2) After the reactor cooled to room temperature, the inner liner of the reactor was opened. The obtained precipitate was washed three times with deionized water and dried in a 60°C forced-air drying oven for 12 hours. Subsequently, the material was transferred to a muffle furnace and calcined at 900°C for 5 hours to obtain a particle size and pore size of 3–8 μm and 3–32 nm, respectively, and a specific surface area of ​​259 m². 2 / g of mesoporous titanium niobium oxide material;

[0070] (3) 0.7 g of elemental sulfur and 0.3 g of titanium niobium oxide were mixed in isopropanol solution at room temperature with a material-to-liquid mass ratio of 1:4. The mixture was magnetically stirred for 15 min and then poured into a high-pressure reactor with a polytetrafluoroethylene liner. The mixture was subjected to a solvothermal reaction at 150 °C for 24 h. After the reaction, the reactor was opened, and the mixture was then filtered and dried at 100 °C for 5 h to obtain a sulfur-titanium niobium oxide composite material.

[0071] (4) Toluene (containing 91.3% carbon) was sealed inside a glass container with a gas valve. The sulfur-titanium niobium oxide composite material obtained in step (3) was placed inside the plasma generator cavity. The vacuum pump was turned on to evacuate the plasma generator cavity to a vacuum level of 20 Pa. The plasma generator was then turned on. When the temperature inside the cavity reached 150°C, the radio frequency power supply was turned on and the radio frequency power was adjusted to 100W. The reaction was carried out under these conditions for 15 minutes to obtain a carbon-coated sulfur-titanium niobium oxide composite cathode material, in which the sulfur element accounted for 67 wt.% of the total composite cathode material, the titanium niobium oxide accounted for 28 wt.%, and the carbon element accounted for 5 wt.%.

[0072] Example 5

[0073] (1) Mix 0.318g tetraethyl titanate (purity 99%), 1.5g niobium oxalate (purity 99%) and 0.073g polystyrene in isopropanol solution at room temperature 25°C with a material-to-liquid mass ratio of 1:4. Stir magnetically for 15min. Pour the mixed solution into a polytetrafluoroethylene inner liner. Then place the inner liner into a high-pressure reactor and carry out a solvothermal reaction at 180°C for 16h.

[0074] (2) After the reactor cooled to room temperature, the inner liner of the reactor was opened. The obtained precipitate was washed three times with deionized water and dried in an 80°C forced-air drying oven for 8 hours. Subsequently, the material was transferred to a muffle furnace and calcined at 700°C for 10 hours to obtain a particle size and pore size of 2–5 μm and 7–42 nm, respectively, with a specific surface area of ​​158 m². 2 / g of mesoporous titanium niobium oxide material;

[0075] (3) 0.8 g of elemental sulfur and 0.2 g of titanium niobium oxide were mixed in an ethanol solution at room temperature with a material-to-liquid mass ratio of 1:4. The mixture was magnetically stirred for 15 min and then poured into a high-pressure reactor with a polytetrafluoroethylene liner. The mixture was subjected to a solvothermal reaction at 160 °C for 20 h. After the reaction, the reactor was opened, and the mixture was then filtered and dried at 60 °C for 14 h to obtain a sulfur-titanium niobium oxide composite material.

[0076] (4) Toluene (containing 91.3% carbon) was sealed inside a glass container with a gas valve. The sulfur-titanium niobium oxide composite material obtained in step (3) was placed inside the plasma generator cavity. The vacuum pump was turned on to evacuate the plasma generator cavity to a vacuum level of 10 Pa. The plasma generator was then turned on. When the temperature inside the cavity reached 30°C, the radio frequency power supply was turned on and the radio frequency power was adjusted to 500W. The reaction was carried out under these conditions for 10 minutes to obtain a carbon-coated sulfur-titanium niobium oxide composite cathode material, in which the sulfur element accounted for 78 wt.% of the total composite cathode material, the titanium niobium oxide accounted for 19 wt.%, and the carbon element accounted for 3 wt.%.

[0077] Example 6

[0078] (1) Mix 0.945g tetrabutyl titanate (purity 98%), 1.5g niobium pentachloride (purity 99.9%) and 0.073g polyvinyl alcohol in ethanol solution at room temperature 25°C with a material-to-liquid mass ratio of 1:6. Stir magnetically for 20min. Pour the mixed solution into a polytetrafluoroethylene inner liner. Then place the inner liner into a high-pressure reactor and carry out a solvothermal reaction at 180°C for 12h.

[0079] (2) After the reactor cooled to room temperature, the inner liner of the reactor was opened. The obtained precipitate was washed three times with deionized water and dried in a 60°C forced-air drying oven for 12 hours. Subsequently, the material was transferred to a muffle furnace and calcined at 800°C for 10 hours to obtain a particle size and pore size of 4–5 μm and 1–36 nm, respectively, with a specific surface area of ​​254 m². 2 / g of mesoporous titanium niobium oxide material;

[0080] (3) 0.9 g of elemental sulfur and 0.1 g of titanium niobium oxide were mixed in butanol solution at room temperature with a material-to-liquid mass ratio of 1:6. The mixture was magnetically stirred for 10 min and then poured into a high-pressure reactor with a polytetrafluoroethylene liner. The mixture was subjected to a solvothermal reaction at 160 °C for 16 h. After the reaction, the reactor was opened, and the mixture was then filtered and dried at 60 °C for 10 h to obtain a sulfur-titanium niobium oxide composite material.

[0081] (4) Toluene (containing 91.3% carbon) was sealed inside a glass container with a gas valve. The sulfur-titanium niobium oxide composite material obtained in step (3) was placed inside the plasma generator cavity. The vacuum pump was turned on to evacuate the plasma generator cavity to a vacuum level of 15 Pa. The plasma generator was then turned on. When the temperature inside the cavity reached 60°C, the radio frequency power supply was turned on and the radio frequency power was adjusted to 200W. The reaction was carried out under these conditions for 30 minutes to obtain a carbon-coated sulfur-titanium niobium oxide composite cathode material, in which the sulfur element accounted for 85 wt.% of the total composite cathode material, the titanium niobium oxide accounted for 10 wt.%, and the carbon element accounted for 5 wt.%.

[0082] Comparative Example 1

[0083] The cathode material is elemental sulfur without any treatment.

[0084] Comparative Example 2

[0085] (1) Mix 0.945g tetrabutyl titanate (purity 98%), 1.5g niobium pentachloride (purity 99.9%) and 0.098g polylactic acid in ethanol solution at room temperature 25°C with a material-to-liquid mass ratio of 1:6. Stir magnetically for 20min. Pour the mixed solution into a polytetrafluoroethylene inner liner. Then place the inner liner into a high-pressure reactor and carry out a solvothermal reaction at 180°C for 14h.

[0086] (2) After the reactor cooled to room temperature, the inner liner of the reactor was opened. The obtained precipitate was washed three times with deionized water and dried in a 60°C forced-air drying oven for 12 hours. Then, the material was transferred to a muffle furnace and calcined at 900°C for 8 hours to obtain a particle size and pore size of 3-6 μm and 5-41 nm, respectively, with a specific surface area of ​​100 m². 2 / g of mesoporous titanium niobium oxide material;

[0087] (3) 0.8 g of elemental sulfur and 0.2 g of titanium niobium oxide were mixed in an ethanol solution at room temperature with a material-to-liquid mass ratio of 1:6. The mixture was magnetically stirred for 10 min and then poured into a high-pressure reactor with a polytetrafluoroethylene liner. The mixture was subjected to a solvothermal reaction at 160 °C for 14 h. After the reaction, the reactor was opened, and the mixture was then filtered and dried at 60 °C for 12 h to obtain a sulfur-titanium niobium oxide composite material, in which sulfur accounted for 80 wt.% of the total composite cathode material and titanium niobium oxide accounted for 20 wt.%.

[0088] Battery assembly and performance testing

[0089] (1) Weigh 0.8g of the carbon-coated sulfur-titanium niobium oxide composite cathode material obtained in Example 1, 0.1g of conductive carbon black (Super P, particle size 40nm, purity 99.9%, Aladdin), 0.1g of binder PVDF (particle size 5μm, purity 99.9%, Aladdin), and 2.33g of solvent N-methylpyrrolidone (analytical grade, purity >99.0%, Aladdin) and place them in a glass bottle. Homogenize twice on a homogenizer at a speed of 1780r / min to obtain a cathode slurry with suitable viscosity. Finally, use a 150μm scraper to evenly coat it onto the surface of aluminum foil and place it in a forced-air drying oven to dry at 60℃ for 12h to obtain the carbon-coated sulfur-titanium niobium oxide composite cathode material cathode sheet.

[0090] Examples 2-6 and Comparative Examples 1 and 2 all prepared positive electrode sheets using the above method.

[0091] (2) The positive electrode sheet from step (1) is rolled and stamped under the same conditions to obtain a positive electrode sheet with a diameter of 12 mm. The battery is then assembled in a glove box filled with argon gas, with humidity and oxygen concentration below 0.01 ppm. The assembly process is as follows: positive electrode shell, positive electrode sheet, separator (Celgard 2400 type), electrolyte (1M LiTFSI + DOL:DME (volume ratio 1:1) + 2wt.% LiNO3), lithium sheet, gasket, spring sheet, and negative electrode shell. Finally, the battery is placed on a button cell sealing machine and sealed at 50 kg / cm². 2 After sealing the battery with pressure, leave it overnight.

[0092] (3) Place the button batteries with different positive electrodes that were left overnight in step (2) on a battery charge-discharge tester. The charge-discharge test voltage is 1.7 to 2.8V, and the rate test current is 0.1C, 0.2C, 0.5C, 1C, and 2C.

[0093] Titanium niobium oxide materials were prepared according to the above method, and the results are shown in Table 1.

[0094] Table 1 Comparison of surface morphology of different titanium niobium oxide materials

[0095]

[0096] Porous titanium-niobium oxides prepared by solvothermal reaction have a microstructure greater than 100 μm. 2 The titanium niobium oxide material exhibits a high specific surface area ( / g), a particle size ranging from 2 to 8 μm, and all pores are mesoporous, thus providing sufficient space for subsequent sulfur storage. The specific surface area of ​​the titanium niobium oxide significantly decreases after sulfur infiltration, indicating that elemental sulfur diffuses into the pores of the titanium niobium oxide through melt diffusion.

[0097] The battery was prepared and its performance was measured according to the above method. The results are shown in Table 2.

[0098] Table 2 Comparison of electrochemical performance of different carbon-coated sulfur-titanium-niobium oxide composite cathode materials

[0099]

[0100]

[0101] The carbon-coated sulfur-titanium niobium oxide composite cathode material in Example 1 exhibited an initial discharge capacity of 1156.12 mAh / g and an initial coulombic efficiency of 93.1% during the first cycle at 0.1C. Even under high-rate conditions (2C), the battery capacity remained as high as 525.97 mAh / g. Examples 2-6 showed the same performance trend as Example 1. In Comparative Examples 1 and 2, pure elemental sulfur and the uncoated sulfur-titanium niobium oxide cathode material exhibited lower discharge capacities and lower coulombic efficiencies, resulting in lower capacity and short circuits at high rates. Therefore, the carbon-coated sulfur-titanium niobium oxide composite cathode material possesses a well-formed coating structure, significantly improving the overall conductivity of the material and demonstrating excellent rate performance.

[0102] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims, and all such variations and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for preparing a carbon-coated sulfur-titanium niobium oxide composite cathode material, characterized in that, The steps include the following: (1) The titanium precursor and the niobium precursor are uniformly mixed in an organic solvent, an additive is added, and a solvothermal reaction is carried out; the additive is at least one of polystyrene, polyvinyl alcohol and polylactic acid. (2) The obtained precipitate was calcined to obtain titanium niobium oxide material; the titanium niobium oxide material had a specific surface area of ​​100-300 m². 2 / g, pore size 1-50nm, particle size 2-8μm; (3) Elemental sulfur and titanium niobium oxide materials are uniformly mixed in an organic solvent and subjected to a solvothermal reaction to obtain sulfur-titanium niobium oxide composite material. (4) Using benzene-based substances as carbon source, carbon material is coated on the surface of sulfur-titanium niobium oxide composite material by plasma method to obtain carbon-coated sulfur-titanium niobium oxide composite cathode material; wherein the sulfur element accounts for 67-88 wt.% of the total composite cathode material, the titanium niobium oxide accounts for 10-28 wt.% and the carbon element accounts for 2-5 wt.%.

2. The method for preparing a carbon-coated sulfur-titanium niobium oxide composite cathode material according to claim 1, characterized in that, In step (1), the titanium precursor is at least one of tetrabutyl titanate and tetraethyl titanate; the niobium precursor is at least one of niobium pentachloride and niobium oxalate; and the amount of additive is 3 to 5 wt.% of the total mass of the titanium precursor and the niobium precursor.

3. The method for preparing a carbon-coated sulfur-titanium niobium oxide composite cathode material according to claim 1, characterized in that, In step (1), the conditions for the solvothermal reaction are: the organic solvent is at least one of ethanol, ethylene glycol, isopropanol and butanol, the reaction temperature is 140-180℃, the reaction time is 8-20h, and the mass ratio of the liquid to the material is 1:4-1:

8.

4. The method for preparing a carbon-coated sulfur-titanium niobium oxide composite cathode material according to claim 1, characterized in that, In step (2), the calcination conditions are: calcination temperature of 700-900℃, calcination time of 5-10h, and heating rate of 2-5℃ / min.

5. The method for preparing a carbon-coated sulfur-titanium niobium oxide composite cathode material according to claim 1, characterized in that, In step (3), the mass ratio of elemental sulfur to titanium niobium oxide is 7:3 to 9:1, and the conditions for the solvothermal reaction are: the organic solvent is at least one of ethanol, ethylene glycol, isopropanol, butanol and carbon disulfide, the reaction temperature is 140 to 180°C, the reaction time is 12 to 24 h, and the mass ratio of material to liquid is 1:4 to 1:

8.

6. The method for preparing a carbon-coated sulfur-titanium niobium oxide composite cathode material according to claim 1, characterized in that, In step (4), the carbon source is at least one of benzene, toluene, ethylbenzene and xylene. The plasma carbon coating reaction conditions include: vacuuming to a vacuum degree of 10-30 Pa, heating temperature of 30-150 °C, radio frequency power of 100-500 W, and reaction time of 5-30 min.

7. A carbon-coated sulfur-titanium niobium oxide composite cathode material prepared by the method according to any one of claims 1-6.

8. The application of a carbon-coated sulfur-titanium niobium oxide composite cathode material prepared by the preparation method according to any one of claims 1-6 in the field of lithium metal batteries.

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