A method for preparing phosphorus-doped sulfur nanoparticles and their application

Abstract

This invention discloses a method for preparing and applying phosphorus-doped sulfur nanoparticles. In these nanoparticles, phosphorus is uniformly distributed on the sulfur nanoparticles, forming S-P chemical bonds between them. Utilizing the properties that elemental phosphorus and sulfur are soluble and miscible in ethylenediamine solution, a solution of sulfur and phosphorus in a specific ratio is prepared and added to an organic solution containing a surfactant. A formic acid solution of a certain concentration is then added dropwise to precipitate the product. After washing and freeze-drying, the phosphorus-doped sulfur nanoparticles are obtained. This preparation method avoids high-temperature heating, directly forming P-S bonds through a wet chemical method to achieve phosphorus doping of sulfur. It boasts a high yield and can be mass-produced. The nano-sized phosphorus-doped sulfur particles, due to their excellent properties such as high specific surface area and nanoscale effect, can be applied in energy storage fields such as lithium-sulfur batteries, exhibiting excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of materials technology, specifically to a method for preparing and applying phosphorus-doped sulfur nanoparticles. Background Technology

[0002] To meet the current demand for new battery systems with long cycle life, high energy density, and high rate performance, lithium-sulfur batteries are gradually gaining popularity. Compared to traditional lithium-ion batteries, lithium-sulfur batteries have advantages such as high theoretical capacity (1675 mAh g−1), high energy density (2600 Wh kg−1), abundant resources, and low cost.

[0003] However, there are still many problems to be solved before lithium-sulfur batteries can be put into practical application: (1) The ionic / electronic conductivity of elemental sulfur and its polysulfides is poor, resulting in low utilization of active materials; (2) The volume change of elemental sulfur during charging and discharging is large, which can easily lead to electrode pulverization and affect cycle stability; (3) The small volume of polysulfide molecules makes it easy to penetrate the membrane and react directly with lithium metal (lithium-sulfur shuttle effect), which seriously affects its coulombic efficiency and cycle stability; (4) The redox kinetics of elemental sulfur is relatively slow, which seriously affects its rate performance.

[0004] To overcome these problems, structural design of the sulfur cathode is necessary. Some carbon materials, such as microporous and mesoporous carbon, can form core-shell hollow nanostructures as sulfur carriers. However, due to the weak interaction between sulfur and carbon-based materials, polysulfides can only be anchored through physical confinement, resulting in poor suppression of the polysulfide shuttle effect and insufficient cycle stability. To increase the polarity of carbon materials, elemental doping (e.g., nitrogen, oxygen, boron, and phosphorus) is considered a solution. Elemental doping can significantly increase the sulfur fixation effect of carbon carrier materials and also has a certain effect on polysulfide catalytic conversion, greatly improving the electrochemical performance of lithium-sulfur batteries. Recently, polar transition metal compounds, including metal oxides, metal sulfides, metal selenides, and metal phosphides, are also considered good carriers for elemental sulfur due to their strong chemical interactions with polysulfides and their catalytic conversion effect. There are various methods for impurity atom doping of carbon materials, such as treatment with different acids, treatment under different atmospheres, or designing polymer precursors before carbonization. These methods are all too complex and energy-intensive, making them unsuitable for large-scale production and application.

[0005] To address the above issues, those skilled in the art urgently need to provide a method for preparing and applying phosphorus-doped sulfur nanoparticles. This method directly dops elemental sulfur with phosphorus to form PS chemical bonds, thereby enabling the mass production of phosphorus-doped sulfur nanoparticles. These nanoparticles exhibit excellent electrochemical performance when applied to the cathode of lithium-sulfur batteries, making it possible for the large-scale production of lithium-sulfur batteries. The process is simple, the raw materials are readily available, and the nanoparticles can be produced on a large scale. They also exhibit excellent electrochemical performance and have broad application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing and applying phosphorus-doped sulfur nanoparticles. By directly doping elemental sulfur with phosphorus to form PS chemical bonds, phosphorus-doped sulfur nanoparticles can be produced in large quantities. When applied to the cathode of lithium-sulfur batteries, they exhibit excellent electrochemical performance, making it possible to scale up the production of lithium-sulfur batteries. The process is simple, the raw materials are readily available, and the electrochemical performance is excellent, with broad application prospects.

[0007] This invention provides a method for preparing phosphorus-doped sulfur nanoparticles, comprising the following steps:

[0008] Step a: Add a certain amount of red phosphorus to an ethylenediamine solution, heat and stir in an oil bath for 6-12 hours to obtain a red phosphorus ethylenediamine solution;

[0009] Step b: Add a certain amount of elemental sulfur powder to the ethylenediamine solution and stir magnetically for 2-3 hours to obtain a sulfur ethylenediamine solution;

[0010] Step c: Slowly add a certain concentration of red phosphorus ethylenediamine solution to thioethylenediamine solution and stir magnetically for 2-3 hours to obtain a uniform mixed solution of red phosphorus and thioethylenediamine.

[0011] Step d: Slowly add a certain amount of polyvinylpyrrolidone to N,N-dimethylformamide solution and stir magnetically for 2-3 hours to obtain a homogeneous solution M; Slowly add the mixed solution of red phosphorus and thioethylenediamine from step c to solution M and stir magnetically for 2-3 hours to obtain a homogeneous solution A; Under magnetic stirring, add formic acid solution to homogeneous solution A to precipitate the product.

[0012] Step e: Wash the product precipitated in step d repeatedly with deionized water and alcohol, and then freeze-dry the pre-frozen sample for a preset time to obtain phosphorus-doped sulfur nanoparticles, which are used in lithium-sulfur batteries.

[0013] The phosphorus-doped sulfur nanoparticles contain the following components in the following mass percentages: 3-9 wt% phosphorus and 91-97 wt% sulfur; the phosphorus element in the phosphorus-doped sulfur nanoparticles is uniformly distributed on the sulfur nanoparticles, and SP chemical bonds are formed between the two.

[0014] Preferably, in step a, 1g of red phosphorus powder is added to 5ml of ethylenediamine solution, and a homogeneous and stable red phosphorus ethylenediamine solution with a concentration of 200mg / ml is prepared under oil bath conditions at 80-120℃.

[0015] Preferably, in step b, 1g of elemental sulfur powder is added to 5ml of ethylenediamine solution and magnetically stirred for 2h to prepare a homogeneous and stable ethylenediamine solution with a concentration of 200mg / ml.

[0016] Preferably, in step c, 0.6 ml of red phosphorus ethylenediamine solution is added to 5 ml of thioethylenediamine solution and magnetically stirred for 2 hours to obtain a mixed solution of red phosphorus and thioethylenediamine, wherein the ratio of red phosphorus to thioethylenediamine is P:S=3:25.

[0017] Preferably, in step d, 100 mg of polyvinylpyrrolidone is added to an N,N-dimethylformamide solution, then 5 ml of a mixed solution of red phosphorus and thioethylenediamine is added to the above solution, the mixture is magnetically stirred for 2 hours, and 1 ml of formic acid solution is added dropwise to the mixed solution.

[0018] Preferably, in step e, the precipitated product is washed multiple times with alcohol and deionized water until the pH of the supernatant is <8, and then freeze-dried to obtain the target product.

[0019] Preferably, in step e, the product is pre-frozen at -25 to -48°C for 8 to 24 hours, and then freeze-dried at -40 to -60°C for 24 to 48 hours to obtain the target product.

[0020] Preferably, the phosphorus-doped sulfur nanoparticles have a nanospherical morphology and a particle size of 100-500 nm.

[0021] The present invention also provides an application of phosphorus-doped sulfur nanoparticles prepared by the above preparation method in lithium-sulfur batteries.

[0022] The present invention provides a method for preparing and applying phosphorus-doped sulfur nanoparticles, which has the following advantages:

[0023] 1. This invention utilizes the properties that elemental phosphorus and sulfur are soluble and miscible in ethylenediamine solution to directly dope elemental sulfur with phosphorus to form PS chemical bonds. The target product exhibits a nanosphere morphology, enabling the mass production of phosphorus-doped sulfur nanoparticles, providing a potential option for the large-scale production of lithium-sulfur batteries. 2. This invention employs a wet chemical method to prepare phosphorus-doped sulfur nanoparticles. First, red phosphorus and elemental sulfur are dissolved separately in ethylenediamine solution, with red phosphorus requiring dissolution via an oil bath. Then, the dissolved red phosphorus ethylenediamine solution and the sulfur ethylenediamine solution are mixed in a specific ratio to obtain a homogeneous mixed ethylenediamine solution of red phosphorus and elemental sulfur. The above solution is then slowly added to an N,N-dimethylformamide (DMF) solution containing polyvinylpyrrolidone (PVP) surfactant. In the solution, formic acid solution is slowly added to precipitate the product, and then the product is washed and freeze-dried to obtain phosphorus-doped sulfur nanoparticles; the raw materials are readily available, the process is simple, it can be produced on a large scale, and the application prospects are broad; 3. With the assistance of the surfactant polyvinylpyrrolidone (PVP) in DMF solution, the morphology of the target product can be controlled. The phosphorus-doped sulfur nanoparticles exhibit a spherical morphology with a particle size of about 100 nm. They can be directly melt-loaded with unmodified carbon materials such as Ketjen black for use as the positive electrode of lithium-sulfur batteries. The specific capacity and cycle stability they exhibit are far superior to the control sample without phosphorus doping; 4. The preparation method in this invention avoids high-temperature heating and directly forms PS chemical bonds through wet chemical method to achieve phosphorus doping of sulfur. Its yield is high and it can achieve mass production. Nanoscale phosphorus-doped sulfur particles, due to their excellent properties such as high specific surface area and nanoscale size effect, can be applied in energy storage fields such as lithium-sulfur batteries, exhibiting excellent electrochemical performance; 5. In this invention, the nanoscale phosphorus-doped sulfur particles facilitate thorough mixing with carbon materials, thereby achieving a more uniform loading after molten sulfur loading. The phosphorus element doped in elemental sulfur can adsorb polysulfides and catalyze the conversion of polysulfides; phosphorus-doped sulfur nanoparticles exhibit excellent electrochemical performance when applied to the cathode of lithium-sulfur batteries; 6. This invention directly dops elemental sulfur with phosphorus for use in the cathode of lithium-sulfur batteries, avoiding the complex modification steps commonly used in current methods for elemental sulfur-loaded substrates, thus providing a possibility for the large-scale production of lithium-sulfur batteries. Attached Figure Description

[0024] Figure 1 The XRD pattern of NP-S prepared in Example 1 is shown.

[0025] Figure 2 The SEM image of NP-S prepared for Example 1.

[0026] Figure 3 The SEM image of NP-S prepared for Example 2.

[0027] Figure 4 The EDS spectrum of NP-S prepared for Example 1.

[0028] Figure 5 SEM images of NP-S / C prepared for Example 1.

[0029] Figure 6 The EDS spectrum of NP-S / C prepared for Example 1.

[0030] Figure 7 The elemental composition diagram of NP-S / C prepared for Example 1.

[0031] Figure 8 XPS spectrum of NP-S prepared for Example 1.

[0032] Figure 9 Cyclic stability plot of the NP-S / C assembled coin half-cell prepared for Example 5 at a current density of 1 A / g. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0034] This invention provides phosphorus-doped sulfur nanoparticles, which comprise the following components by mass percentage: 3-9 wt% phosphorus and 91-97 wt% sulfur; the phosphorus element in the phosphorus-doped sulfur nanoparticles is uniformly distributed on the sulfur nanoparticles, and SP chemical bonds are formed between them. The phosphorus-doped sulfur nanoparticles exhibit a nanospherical morphology with a particle size of 100-500 nm.

[0035] This invention directly dops elemental sulfur with phosphorus to form PS chemical bonds, and the target product exhibits a nanosphere morphology. This allows for the mass production of phosphorus-doped sulfur nanoparticles, providing a potential option for the large-scale production of lithium-sulfur batteries.

[0036] This invention also provides a method for preparing phosphorus-doped sulfur nanoparticles, comprising the following steps:

[0037] Step a: Add a certain amount of red phosphorus to an ethylenediamine solution, heat and stir in an oil bath for 6-12 hours to obtain a red phosphorus ethylenediamine solution.

[0038] One method involved adding 1g of red phosphorus powder to 5ml of ethylenediamine solution and preparing a homogeneous and stable red phosphorus ethylenediamine solution with a concentration of 200mg / ml under oil bath conditions at 80-120℃.

[0039] In step a, the high-temperature oil bath helps red phosphorus dissolve in ethylenediamine solvent. The self-ionization of amino anions attacks the empty 3d orbitals of red phosphorus molecules, thereby forming polyphosphoric ions (P4).

[0040] Step b: Add a certain amount of elemental sulfur powder to the ethylenediamine solution and stir magnetically for 2-3 hours to obtain a sulfur ethylenediamine solution.

[0041] One method involved adding 1g of elemental sulfur powder to 5ml of ethylenediamine solution and stirring magnetically for 2 hours to prepare a homogeneous and stable ethylenediamine solution with a concentration of 200mg / ml.

[0042] In step b, an ethylenediamine disulfide (H2NCH2CH2NH2-SS-NH2CH2CH2NH2) is formed, in which sulfur replaces the hydrogen atom in ethylenediamine. + .

[0043] Step c: Slowly add a certain concentration of red phosphorus ethylenediamine solution to a thioethylenediamine solution and stir magnetically for 2-3 hours to obtain a uniform mixed solution of red phosphorus and thioethylenediamine.

[0044] In this process, 0.6 ml of red phosphorus ethylenediamine solution was added to 5 ml of thioethylenediamine solution and magnetically stirred for 2 hours to obtain a mixed solution of red phosphorus and thioethylenediamine. The ratio of red phosphorus to thioethylenediamine mixed solution was P:S=3:25.

[0045] In step c, the red phosphorus ethylenediamine solution and the thioethylenediamine solution have similar chemical structures and exhibit the property of being miscible.

[0046] Step d: Slowly add a certain amount of polyvinylpyrrolidone to N,N-dimethylformamide solution and stir magnetically for 2-3 hours to obtain a homogeneous solution M; Slowly add the mixed solution of red phosphorus and thioethylenediamine from step c to solution M and stir magnetically for 2-3 hours to obtain a homogeneous solution A; Under magnetic stirring, add formic acid solution to homogeneous solution A to precipitate the product.

[0047] In this process, 100 mg of polyvinylpyrrolidone was added to an N,N-dimethylformamide solution, and then 5 ml of a mixed solution of red phosphorus and thioethylenediamine was added to the above solution. The mixture was magnetically stirred for 2 hours, and then 1 ml of 9M formic acid solution was slowly added dropwise to the mixed solution.

[0048] In step d, polyvinylpyrrolidone (PVP) acts as a surfactant to control the morphology of phosphorus-doped sulfur nanoparticles. N,N-dimethylformamide (DMF) solution, with its larger molecular weight compared to deionized water, increases the steric hindrance to polymerization between nanoparticles, thus inhibiting agglomeration of the phosphorus-doped sulfur nanoparticles. The addition of formic acid results in excess H₂ in the solution. + It attacks the S and P elements in a mixed solution of red phosphorus and thioethylenediamine, causing them to precipitate and form PS bonds.

[0049] Step e: Wash the product precipitated in step d repeatedly with deionized water and alcohol, and then freeze-dry the pre-frozen sample for a preset time to obtain phosphorus-doped sulfur nanoparticles.

[0050] The precipitated product was washed multiple times with alcohol and deionized water until the pH of the supernatant was <8, and then freeze-dried to obtain the target product. The purpose was to remove residual ethylenediamine from the product and prevent the agglomeration of nanoparticles during the freeze-drying process.

[0051] In addition, the product is pre-frozen at -25 to -48°C for 8 to 24 hours, and then freeze-dried at -40 to -60°C for 24 to 48 hours to obtain the NP-S target product. Pre-freezing with deionized water allows ice crystals to be uniformly filled between the NP-S products, preventing the agglomeration of nanoparticles during freeze-drying.

[0052] This invention employs a wet chemical method to prepare phosphorus-doped sulfur nanoparticles. First, red phosphorus and elemental sulfur are dissolved separately in ethylenediamine solutions, with the red phosphorus requiring dissolution via an oil bath. Then, the dissolved red phosphorus ethylenediamine solution and the sulfur ethylenediamine solution are mixed in a specific ratio to obtain a homogeneous mixed ethylenediamine solution of red phosphorus and elemental sulfur. This solution is then slowly added to an N,N-dimethylformamide (DMF) solution containing polyvinylpyrrolidone (PVP) surfactant. Formic acid solution is then slowly added to precipitate the product. The product is then washed and freeze-dried to obtain phosphorus-doped sulfur nanoparticles. The raw materials are readily available, the process is simple, and it can be mass-produced with broad application prospects.

[0053] With the assistance of the surfactant polyvinylpyrrolidone (PVP) in DMF solution, the morphology of the target product can be controlled. Phosphorus-doped sulfur nanoparticles exhibit a spherical morphology with a particle size of approximately 100 nm. They can be directly melt-loaded with unmodified carbon materials such as Ketjen Black for use as cathodes in lithium-sulfur batteries, exhibiting significantly better specific capacity and cycle stability than the control sample without phosphorus doping. The preparation method in this invention avoids high-temperature heating, directly forming PS chemical bonds through a wet chemical method to achieve phosphorus-doped sulfur, with high yield, enabling mass production. The nano-sized phosphorus-doped sulfur particles, due to their excellent properties such as high specific surface area and nanoscale effect, can be applied in energy storage fields such as lithium-sulfur batteries, exhibiting excellent electrochemical performance.

[0054] This invention also provides the application of the above-mentioned phosphorus-doped sulfur nanoparticles, or phosphorus-doped sulfur nanoparticles prepared by the above-mentioned method, in lithium-sulfur batteries. This invention directly dops elemental sulfur with phosphorus for use as the cathode in lithium-sulfur batteries, avoiding the complex modification steps commonly used in current methods for elemental sulfur-supported substrates, thus enabling the large-scale production of lithium-sulfur batteries. Example 1

[0055] This embodiment provides phosphorus-doped sulfur nanoparticles (NP-S), which comprise the following components by mass percentage: 8 wt% phosphorus and 92 wt% sulfur. The phosphorus element in the phosphorus-doped sulfur nanoparticles is uniformly distributed on the sulfur nanoparticles, and SP chemical bonds are formed between them. The phosphorus-doped sulfur nanoparticles exhibit a nanospherical morphology with a particle size of 100-500 nm.

[0056] This embodiment also provides a method for preparing phosphorus-doped sulfur nanoparticles, including the following steps:

[0057] Step a: Add 1g of red phosphorus powder to 5ml of ethylenediamine solution and prepare a homogeneous and stable red phosphorus ethylenediamine solution with a concentration of 200mg / ml under oil bath conditions at 100℃.

[0058] Step b: Add 1g of elemental sulfur powder to 5ml of ethylenediamine solution and stir magnetically for 2h to prepare a homogeneous and stable ethylenediamine solution with a concentration of 200mg / ml.

[0059] Step c: Add 0.6 ml of red phosphorus ethylenediamine solution to 5 ml of thioethylenediamine solution and stir magnetically for 2 hours to obtain a uniform mixed solution of red phosphorus and thioethylenediamine. The ratio of red phosphorus to thioethylenediamine mixed solution is P:S=3:25.

[0060] Step d: Slowly add 100 mg of polyvinylpyrrolidone to 20 ml of N,N-dimethylformamide solution and stir magnetically for 2 h to obtain a homogeneous solution M; Slowly add the mixed solution of red phosphorus and thioethylenediamine from step c to solution M and stir magnetically for 2 h to obtain a homogeneous solution A; Under magnetic stirring, add 1 ml of formic acid solution to homogeneous solution A to precipitate NP-S.

[0061] Step e: Wash the product precipitated in step d repeatedly with deionized water and alcohol until the pH of the supernatant is <8. Then, pre-freeze it at -30°C for 8 hours and freeze-dry it at -40°C for 48 hours to obtain phosphorus-doped sulfur nanoparticles.

[0062] Figure 1 The XRD pattern of NP-S prepared in Example 1 is shown. The characteristic diffraction peaks of NP-S in the figure match well with the characteristic peaks of elemental sulfur (PDF#08-0247), indicating that the synthesis of NP-S was successful and the basic phase is S.

[0063] Figure 2SEM images of the NP-S prepared in Example 1 are shown. As shown, the NP-S prepared in Example 1 exhibits a distinct spherical morphology with a size ranging from 100 to 500 nm. The spherical morphology has the largest specific surface area compared to other morphologies, which helps to obtain a more uniform NP-S / C composite product in the subsequent melt-loading sulfur step.

[0064] Figure 4 The EDS spectrum of NP-S prepared in Example 1 is shown in the figure. As shown, P and S elements are uniformly distributed in the NP-S product without aggregation, further demonstrating the successful synthesis of NRP-S.

[0065] Figure 5 SEM images of the NP-S / C prepared for Example 1 are shown. As shown in the figure, after molten sulfur loading, NP-S in the NP-S / C composite product is uniformly combined with elemental carbon, and its corresponding EDS spectrum is shown. Figure 6 In the sample, elements such as P, S, and C are evenly distributed, and the mass fraction of the corresponding elements is ( ). Figure 7 The concentrations were 0.9%, 66.1%, and 33%, respectively. In summary, the NP-S / C composite product was successfully prepared, and phosphorus was successfully doped. The uniform composite formation of the NP-S / C composite product helps improve the overall conductivity of the composite material, and the successful doping of phosphorus promotes the adsorption and catalytic conversion of polysulfides, which will greatly enhance the electrochemical performance of the NP-S / C composite product.

[0066] Figure 8 XPS spectrum of NP-S prepared for Example 1. Figure 8 (a) shows the high-resolution spectrum of S 2p. The two peaks at 163.2 and 162.6 eV correspond to the SS and PS bonds, respectively, indicating that P and S elements are bonded in the NP-S composite product. Meanwhile, in the high-resolution spectrum of P 2p, the two characteristic peaks at 128.6 and 131.4 eV can be attributed to the PS and PP bonds, indicating the presence of P elements in the NP-S composite product. In conclusion, the NP-S composite product was successfully synthesized, and P and S elements formed chemical bonds. Example 2

[0067] This embodiment provides phosphorus-doped sulfur nanoparticles (NP-S), which comprise the following components by mass percentage: 9 wt% phosphorus and 91 wt% sulfur. The phosphorus element in the phosphorus-doped sulfur nanoparticles is uniformly distributed on the sulfur nanoparticles, and SP chemical bonds are formed between them. The phosphorus-doped sulfur nanoparticles exhibit a nanospherical morphology with a particle size of 100-500 nm.

[0068] This embodiment also provides a method for preparing phosphorus-doped sulfur nanoparticles, including the following steps:

[0069] Step a: Add 1g of red phosphorus powder to 5ml of ethylenediamine solution and prepare a homogeneous and stable red phosphorus ethylenediamine solution with a concentration of 200mg / ml under oil bath conditions at 80℃.

[0070] Step b: Add 1g of elemental sulfur powder to 5ml of ethylenediamine solution and stir magnetically for 2h to prepare a homogeneous and stable ethylenediamine solution with a concentration of 200mg / ml.

[0071] Step c: Add 0.6 ml of red phosphorus ethylenediamine solution to 5 ml of thioethylenediamine solution and stir magnetically for 2 hours to obtain a uniform mixed solution of red phosphorus and thioethylenediamine. The ratio of red phosphorus to thioethylenediamine mixed solution is P:S=3:25.

[0072] Step d: Slowly add 100 mg of polyvinylpyrrolidone to 20 ml of N,N-dimethylformamide solution and stir magnetically for 3 h to obtain a homogeneous solution M; Slowly add the mixed solution of red phosphorus and thioethylenediamine from step c to solution M and stir magnetically for 3 h to obtain a homogeneous solution A; Under magnetic stirring, slowly add 1 ml of 9M formic acid solution to homogeneous solution A to precipitate NP-S.

[0073] Step e: Wash the NP-S precipitate obtained in step d repeatedly with deionized water and alcohol until the pH of the supernatant is <8. Then, pre-freeze it at -25℃ for 12 hours and freeze-dry it at -50℃ for 40 hours to obtain phosphorus-doped sulfur nanoparticles.

[0074] Figure 3 SEM images of NP-S prepared in Example 2. Compared with Example 1, the NP-S product obtained without the addition of PVP exhibits a large blocky morphology, indicating that PVP has the effect of regulating the morphology of NP-S product. Example 3

[0075] This embodiment provides phosphorus-doped sulfur nanoparticles (NP-S), which contain the following components by mass percentage: 3 wt% phosphorus and 97 wt% sulfur. The phosphorus element in the phosphorus-doped sulfur nanoparticles is uniformly distributed on the sulfur nanoparticles, and SP chemical bonds are formed between them. The phosphorus-doped sulfur nanoparticles exhibit a nanospherical morphology with a particle size of 100-500 nm.

[0076] This embodiment also provides a method for preparing phosphorus-doped sulfur nanoparticles, including the following steps:

[0077] Step a: Add 1g of red phosphorus powder to 5ml of ethylenediamine solution and prepare a homogeneous and stable red phosphorus ethylenediamine solution with a concentration of 200mg / ml under oil bath conditions at 120℃.

[0078] Step b: Add 1g of elemental sulfur powder to 5ml of ethylenediamine solution and stir magnetically for 2h to prepare a homogeneous and stable ethylenediamine solution with a concentration of 200mg / ml.

[0079] Step c: Add 0.4 ml of red phosphorus ethylenediamine solution to 5 ml of thioethylenediamine solution and stir magnetically for 2 hours to obtain a uniform mixed solution of red phosphorus and thioethylenediamine. The ratio of red phosphorus to thioethylenediamine mixed solution is P:S=2:25.

[0080] Step d: Slowly add 100 mg of polyvinylpyrrolidone to 20 ml of N,N-dimethylformamide solution and stir magnetically for 2 h to obtain a homogeneous solution M; Slowly add the mixed solution of red phosphorus and thioethylenediamine from step c to solution M and stir magnetically for 2 h to obtain a homogeneous solution A; Under magnetic stirring, slowly add 1 ml of 9M formic acid solution to homogeneous solution A to precipitate NP-S.

[0081] Step e: Wash the NP-S precipitate obtained in step d repeatedly with deionized water and alcohol until the pH of the supernatant is <8. Then, pre-freeze it at -48℃ for 10 hours and freeze-dry it at -60℃ for 48 hours to obtain phosphorus-doped sulfur nanoparticles. Example 4

[0082] This embodiment also provides a method for preparing NP-S / C and S / C composite products, comprising the following steps: taking 75 mg of NP-S / S obtained in Example 2 as the active material and grinding it with 25 mg of Ketjen black for 30 min to obtain a mixture of NP-S and Ketjen black. The mixture is then transferred to a crucible and subjected to molten sulfur loading at 155 °C for 12 h in a tube furnace under an argon atmosphere to obtain NP-S / C and S / C composite products respectively. Example 5

[0083] This embodiment also provides a method for preparing an NP-S / C lithium-sulfur battery, including the following steps: 80 mg of the NP-S / C and S / C composite product obtained in Example 4 is used as the active material and 10 mg of conductive carbon black is ground for 30 min. Then, a polyvinylidene fluoride (PVDF) solution with N-methylpyrrolidone (NMP) as the solvent and 0.8 ml of a PVDF solution with a concentration of 12.5 mg / ml are added to the ground mixture. After magnetic stirring for 4 h, an NRP-S / C electrode slurry is obtained. This slurry is coated onto a copper foil and dried in a vacuum oven at 80°C for 12 h to obtain NP-S / C and S / C electrode sheets. The NP-S / C and S / C electrode sheets are used as the positive electrode, pure lithium sheets are used as the negative electrode, the electrolyte is 1.0 M LiTFSI / (DME+DOL) (1:1 vol) with 1 wt% LiNO3 as an additive, and Celgard 2400 is used as the separator. The half-cell is assembled in an argon-atmosphere glove box.

[0084] Figure 9 Figures (a) and (b) show the cycling stability of the NP-S / C and S / C assembled button half-cells prepared in Example 5 at a current density of 1 A / g, respectively. The initial discharge capacity of the NP-S / C electrode was 845 mAh / g, and after 500 cycles, the discharge capacity remained at 573 mAh / g, corresponding to a capacity retention of 68%. In contrast, the discharge capacity of the S / C electrode after 500 cycles was 350 mAh / g, corresponding to a capacity retention of 35%. The NP-S / C electrode exhibited superior electrochemical performance, which is attributed to the more uniform composite of the NP-S / C composite product and the successful doping of phosphorus.

[0085] In summary, the present invention provides a method for preparing and applying phosphorus-doped sulfur nanoparticles. This method directly dops elemental sulfur with phosphorus to form PS chemical bonds, thereby enabling the mass production of phosphorus-doped sulfur nanoparticles. These nanoparticles exhibit excellent electrochemical performance when applied to the cathode of lithium-sulfur batteries, making it possible for the large-scale production of lithium-sulfur batteries. The process is simple, the raw materials are readily available, and the electrochemical performance is excellent, indicating broad application prospects.

[0086] Those skilled in the art can make various modifications and applications without departing from the essential characteristics of the embodiments. For example, each component detailed in the embodiments can be modified and operated, and the differences associated with such modifications and applications can be considered to be included within the scope of protection of the invention as defined in the appended claims.

[0087] The embodiments described in this specification are intended to imply that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. These terms appearing throughout the specification do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is assumed that it falls within the scope of those particular features, structures, or characteristics that could be implemented by one of ordinary skill in the art in conjunction with other embodiments.

Claims

1. A method for preparing phosphorus-doped sulfur nanoparticles, characterized in that, Includes the following steps: Step a: Add a certain amount of red phosphorus to an ethylenediamine solution, heat and stir in an oil bath for 6-12 hours to obtain a red phosphorus ethylenediamine solution; Step b: Add a certain amount of elemental sulfur powder to the ethylenediamine solution and stir magnetically for 2-3 hours to obtain a sulfur ethylenediamine solution; Step c: Slowly add a certain concentration of red phosphorus ethylenediamine solution to thioethylenediamine solution and stir magnetically for 2-3 hours to obtain a uniform mixed solution of red phosphorus and thioethylenediamine. Step d: Slowly add a certain amount of polyvinylpyrrolidone to N,N-dimethylformamide solution and stir magnetically for 2-3 hours to obtain a homogeneous solution M; Slowly add the mixed solution of red phosphorus and thioethylenediamine from step c to solution M and stir magnetically for 2-3 hours to obtain a homogeneous solution A; Under magnetic stirring, add formic acid solution to homogeneous solution A to precipitate the product. Step e: Wash the product precipitated in step d repeatedly with deionized water and alcohol, and then freeze-dry the pre-frozen sample for a preset time to obtain phosphorus-doped sulfur nanoparticles, which are used in lithium-sulfur batteries. The phosphorus-doped sulfur nanoparticles contain the following components in the following mass percentages: 3-9 wt% phosphorus and 91-97 wt% sulfur; the phosphorus element in the phosphorus-doped sulfur nanoparticles is uniformly distributed on the sulfur nanoparticles, and SP chemical bonds are formed between the two.

2. The method for preparing phosphorus-doped sulfur nanoparticles according to claim 1, characterized in that, In step a, 1g of red phosphorus powder is added to 5ml of ethylenediamine solution, and a homogeneous and stable red phosphorus ethylenediamine solution with a concentration of 200mg / ml is prepared under oil bath conditions of 80-120℃.

3. The method for preparing phosphorus-doped sulfur nanoparticles according to claim 1, characterized in that, In step b, 1g of elemental sulfur powder is added to 5ml of ethylenediamine solution and magnetically stirred for 2h to prepare a homogeneous and stable ethylenediamine solution with a concentration of 200mg / ml.

4. The method for preparing phosphorus-doped sulfur nanoparticles according to claim 1, characterized in that, In step c, 0.6 ml of red phosphorus ethylenediamine solution is added to 5 ml of thioethylenediamine solution and magnetically stirred for 2 hours to obtain a mixed solution of red phosphorus and thioethylenediamine. The ratio of red phosphorus to thioethylenediamine mixed solution is P:S=3:

25.

5. The method for preparing phosphorus-doped sulfur nanoparticles according to claim 1, characterized in that, In step d, 100 mg of polyvinylpyrrolidone was added to an N,N-dimethylformamide solution, and then 5 ml of a mixed solution of red phosphorus and thioethylenediamine was added to the above solution. The mixture was magnetically stirred for 2 hours, and then 1 ml of formic acid solution was added dropwise to the mixed solution.

6. The method for preparing phosphorus-doped sulfur nanoparticles according to claim 1, characterized in that, In step e, the precipitated product is washed multiple times with alcohol and deionized water until the pH of the supernatant is <8, and then freeze-dried to obtain the target product.

7. The method for preparing phosphorus-doped sulfur nanoparticles according to claim 6, characterized in that, In step e, the product is pre-frozen in a refrigerator at -25 to -48°C for 8 to 24 hours, and then freeze-dried at -40 to -60°C for 24 to 48 hours to obtain the target product.

8. The method for preparing phosphorus-doped sulfur nanoparticles according to claim 1, characterized in that, The phosphorus-doped sulfur nanoparticles have a nanospherical morphology and a particle size of 100-500 nm.

9. The application of phosphorus-doped sulfur nanoparticles prepared according to any one of claims 1-8 in lithium-sulfur batteries.

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