A modified lithium-sulfur battery diaphragm and its preparation method and application

Abstract

The present invention proposes a modified separator for lithium-sulfur batteries, its preparation method, and its application, belonging to the field of lithium-sulfur batteries. The lithium-sulfur battery assembled with the separator modified with the catalyst Co-NC-P in the present invention has a lower polarization voltage and higher catalytic performance. The rate performance shows that it has 831 mAh g at a rate of 6C. ‑1 After 200 cycles at a current density of 0.5 C, the specific capacity of the battery is still maintained at 963 mAhg ‑1 After 1500 cycles at 2 C current density, it still reached 511 mA h g ‑1 Specific capacity.

Description

Technical Field

[0001] The present invention relates to the field of lithium-sulfur batteries, and in particular to a modified lithium-sulfur battery diaphragm, a preparation method thereof, and applications thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Lithium-sulfur batteries (LiPSs) have excellent energy density (2600 Wh kg -1 ), which is expected to improve the performance of next-generation energy storage batteries. Lithium-sulfur batteries use sulfur as the positive electrode active material and lithium metal sheets as the negative electrode, and have significant advantages: the theoretical specific capacity of sulfur is as high as 1675 mAh g -1 , abundant reserves, low cost and environmentally friendly; the preparation process of sulfur positive electrode is relatively simple. The above characteristics make lithium-sulfur batteries a candidate to replace existing battery technology. However, lithium-sulfur batteries still face many problems in large-scale practical applications. During the battery charging and discharging process, it undergoes complex sulfur redox reactions involving multi-step conversion of polysulfide (LiPSs) intermediates. The slow kinetics of the LiPSs conversion process triggers a shuttle effect, resulting in the accumulation of LiPSs on the negative electrode side and the loss of sulfur active substances, which in turn affects the structural integrity and cycle stability of lithium-sulfur batteries.

[0004] There are currently a variety of regulatory strategies to inhibit the shuttle effect. Among them, introducing catalytic materials into the battery is considered to be an effective way to inhibit the shuttle effect. Functionalizing the diaphragm with catalytic materials can promote the catalytic conversion of polysulfides and improve the capacity and cycle stability of the battery.

[0005] Conventional supported metal particle catalysts are limited in their uniform growth of active sites, making active site exposure difficult and resulting in low atomic utilization efficiency, making it difficult to achieve both high catalytic activity and cost-effectiveness. In contrast, catalysts with atomically dispersed metal sites (ADCs) offer maximum atomic utilization efficiency and excellent catalytic selectivity, and have gradually become a frontier in catalysis research. Single-atom catalysts (SACs), a type of heterogeneous catalyst, not only enable full active site exposure but also possess well-defined structures and uniform active sites, showing promising application prospects in heterogeneous catalysis. In particular, carbon-supported SACs (M-N4) have been reported as catalysts for a variety of reactions, including the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), and sulfur reduction reaction (SRR). The electronic structure of the metal center is known to influence the adsorption and catalytic activity of reaction intermediates. Therefore, modulating the local coordination microenvironment around the metal center atom is considered a promising approach to improving catalytic activity.

[0006] Previous studies have attempted to adjust the catalytic activity of M-Nx sites by changing the local environment of the M-Nx sites by changing the metal center of the M-Nx sites or by adjusting the coordination elements and coordination numbers in the first shell coordination in a short range. For example, Chen et al. reported that N / P-coordinated Fe SACs improved the adsorption of ORR reaction intermediates and enhanced the ORR reaction activity. Xiong et al. prepared an oxygen-nitrogen-coordinated W-N2O2 / NC SACs. The unique electronic structure of the N and O-coordinated W active sites can optimize the binding energy of NRR intermediates, produce products that are conducive to NRR electrocatalysis, and promote the NRR reaction. It can be seen that for the sulfur redox reaction in Li-S batteries, the interaction between the catalyst and LiPSs involves the orbital coupling of the metal and S. Therefore, regulating the adsorption strength of active sites on LiPSs is of great significance for accelerating the kinetics of sulfur redox reactions; compared with the first coordination shell regulation, remote regulation of single-atom metal sites through second-shell coordination is also an effective means to optimize the interaction between LiPSs and metal sites and improve reaction performance, and the degree of regulation is more moderate, avoiding drastic disturbances to the electronic structure of the metal site, and achieving precise regulation of the structure and performance of the metal site.

[0007] In existing research, Chen et al. reported a method for doping P into Co-C3N5, and P was found in the second coordination layer. However, the coordination structure of Co was uncontrollable, and the synthesis process required acid etching to remove the formed Co metal particles, resulting in reduced catalytic activity.

[0008] In the patent application publication number CN118581488A, Co-based carbon-supported single-atom catalysts were studied. By combining molten salt-assisted pyrolysis with ethanol and ethylene glycol post-treatment, the metal active sites were structurally regulated. Rich epoxy groups were introduced into the second coordination shell, and the electronic structure of the active sites and the adsorption behavior of intermediates were optimized at the molecular level. The catalytic path was adjusted from a 4-electron to an optimal 2-electron path, and the synthesis of a highly selective electrochemical H2O2 production catalyst was achieved. Although this patent provides a method for regulating metal atom sites in the second shell coordination, it requires salt dissolution and acid washing, which makes the preparation process complicated. In addition, the coordination structure of the metal site is random, the synthesis process is uncontrollable, and it is not universal.

[0009] In summary, it is currently difficult to achieve precise design of metal atom sites through simple remote regulation of second-shell coordination, and a universal preparation method is still lacking. Therefore, how to efficiently utilize catalyst-prepared battery separators to improve the cycling stability of lithium-sulfur batteries is an urgent issue. Summary of the Invention

[0010] To overcome the shortcomings of the aforementioned prior art, the present invention provides a modified separator for lithium-sulfur batteries, as well as its preparation method and application. By optimizing and controlling catalyst preparation conditions, the present invention develops a universal preparation method. Leveraging molecular confinement, a second-shell phosphorus-coordinated Co-N4 single-atom catalyst (Co-NC-P) is synthesized, achieving precise control of phosphorus doping sites and optimizing catalytic performance. Co-NC-P enhances the adsorption of polysulfides and promotes their rapid conversion. The modified separator for lithium-sulfur batteries prepared using this material effectively addresses the shuttle effect in lithium-sulfur batteries.

[0011] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0012] In a first aspect of the present invention, a modified separator for a lithium-sulfur battery is provided, wherein the modified separator is modified with a second-shell phosphorus atom coordinated Co single-atom catalyst;

[0013] The method for preparing the Co single-atom catalyst coordinated by the second shell phosphorus atom comprises the following steps:

[0014] S1. preparing a solution of 1,10-phenanthroline molecules coordinated with cobalt metal ions;

[0015] S2, preparing phosphorus-doped carbon CP;

[0016] S3. The 1,10-phenanthroline molecule coordinated cobalt metal ion solution is mixed evenly with CP, dried by rotary evaporation, and calcined at high temperature to obtain the second shell phosphorus atom coordinated Co single atom catalyst Co-NC-P.

[0017] In the present invention, o-phenanthroline molecules are used to form Co-N4 structural elements with Co ions, and the first coordination shell structure of Co, namely the Co-N4 structural element, is fixed by molecular confinement. Then, it reacts with a P-doped carbon substrate to avoid P from being incorporated into the first coordination shell of Co in the subsequent process, and instead enters the second coordination shell, thereby achieving precise control.

[0018] In a specific embodiment of the present invention, in step S1, the concentration of the cobalt metal ion solution is 0.01-0.04 mol / L, and the molar concentration ratio of 1,10-phenanthroline to cobalt metal is 2-5:1.

[0019] In a specific embodiment of the present invention, in step S1, the cobalt metal is selected from at least one of cobalt acetate, cobalt acetate tetrahydrate, cobalt nitrate, cobalt carbonate and cobalt chloride.

[0020] In a specific embodiment of the present invention, in step S2, oxygen-doped carbon CO and triphenylphosphine are mixed, calcined at high temperature in an argon-hydrogen atmosphere, and cooled to room temperature to prepare CP; the mass ratio of CO to triphenylphosphine is 1:5, 1:10 or 1:20.

[0021] In a specific embodiment of the present invention, in step S2, the high temperature calcination condition in the argon-hydrogen atmosphere is 8-12 ° C min -1 The temperature is heated to 600-800°C at a rate of 1000 ℃ for 1-4 hours, and then naturally cooled to room temperature to obtain CP.

[0022] In a specific embodiment of the present invention, the CO preparation method is as follows: carbon black is oxidized with nitric acid at 70-90°C in a reflux system for 20-28 hours, cooled to room temperature, washed with ultrapure water and ethanol until the pH of the solution reaches neutral, and then dried in a vacuum oven at 60-90°C.

[0023] In a specific embodiment of the present invention, the amount of carbon black is 0.5-2 g and the concentration of nitric acid is 12 M.

[0024] In a specific embodiment of the present invention, in step S3, 0.5-2 mL of 1,10-phenanthroline molecule coordinated cobalt metal ion solution and 50-100 mg of CP are dispersed in 2.5-7.5 mL of anhydrous ethanol, mixed evenly, and then dried by rotary evaporation and calcined at high temperature to obtain Co-NC-P.

[0025] In a specific embodiment of the present invention, the high-temperature calcination condition is to increase the temperature to 500-900° C. at a rate of 4-8° C. / min in an argon atmosphere, continue heating for 1.5-2 h, and then naturally cool to room temperature.

[0026] The method described in the present invention effectively suppresses the phenomenon of metal ion agglomeration, and fully exposes the catalytic sites without the formation of metal particles, thereby avoiding the subsequent pickling process and metal waste, achieving maximum utilization of metal atoms, and having a simple preparation method and reducing costs.

[0027] The second aspect of the present invention provides a method for preparing a modified separator of a lithium-sulfur battery according to the first aspect, comprising: dispersing a second shell phosphorus atom coordinated Co single-atom catalyst, acetylene black, and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 7:2:1, and mixing thoroughly to obtain a slurry; uniformly coating the slurry on the separator; and drying in a vacuum oven at 60°C for 12 hours to obtain a slurry;

[0028] The membrane included Celgard 2400 membrane.

[0029] The third aspect of the present invention provides use of the modified lithium-sulfur battery separator described in the first aspect in the preparation of a lithium-sulfur battery or a soft-pack battery.

[0030] One or more of the above technical solutions have the following beneficial effects:

[0031] In the present invention, molecular confinement is utilized to precisely introduce P atoms into the second coordination shell of Co-N4. The prepared Co-NC-P catalyst exhibits excellent catalytic conversion performance of sulfur-active substances, can enhance the adsorption of polysulfides, and promote the rapid conversion of polysulfides. Since the coordination of neighboring P atoms regulates the orbits of Co atoms, the reaction energy barrier of the rate-determining step (RDS) can be reduced, the reaction kinetics can be accelerated, the conversion of polysulfides can be promoted, and the shuttle effect caused by it can be inhibited, thereby improving the performance of lithium-sulfur batteries.

[0032] The lithium-sulfur battery assembled with the catalyst Co-NC-P modified separator has lower polarization voltage and higher catalytic performance. The rate performance shows that it has 831 mAh g at 6C rate. -1 After 200 cycles at a current density of 0.5 C, the specific capacity of the battery is still maintained at 963 mAhg -1 After 1500 cycles at 2 C current density, it still reaches 511 mAh g -1 The specific capacity has excellent performance.

[0033] The preparation method of the present invention has simple steps, is economical and efficient, can meet the needs of industrial production, and has potential application value.

[0034] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0036] Figure 1 This is a schematic diagram of the process for preparing the Co-NC-P catalytic material in Experimental Example 1 of the present invention.

[0037] Figure 2 This is the XRD pattern of Co-NC-P prepared in Experimental Example 1 of the present invention.

[0038] Figure 3 This is a low-magnification TEM image of Co-NC-P prepared in Experimental Example 1 of the present invention.

[0039] Figure 4This is the HAADF image of Co-NC-P prepared in Experimental Example 1 of the present invention.

[0040] Figure 5 This is the element distribution diagram of Co-NC-P prepared in Experimental Example 1 of the present invention. The upper left figure is the C element distribution diagram, the upper right figure is the Co element distribution diagram, the lower left figure is the N element distribution diagram, and the lower right figure is the P element distribution diagram.

[0041] Figure 6 This is the X-ray photoelectron spectrum (XPS) of Co-NC-P in Experimental Example 1 of the present invention; wherein, a is the N 1s spectrum of Co-NC and Co-NC-P; b is the Co 2p spectrum of Co-NC and Co-NC-P; c is the P 2p spectrum of Co-NC-P and CP.

[0042] Figure 7 Synchrotron radiation Fourier transform X-ray absorption spectra of Co-NC-P, Co-NC and metal Co foil (Co foil) in the present invention.

[0043] Figure 8 These are the effects of adding Li2S6 electrolyte to Co-NC-P, Co-NC and CP in the present invention and standing for different times, where 1-4 are Li2S6 blank electrolyte, Co-NC-P, Co-NC and CP, respectively.

[0044] Figure 9 This is the cyclic voltammetry curve of the lithium-sulfur battery in Example 1 of the present invention.

[0045] Figure 10 This is the rate performance of the lithium-sulfur battery in Example 1 of the present invention.

[0046] Figure 11 The cycling performance of the lithium-sulfur battery at 0.5 C in Example 1 of the present invention is shown.

[0047] Figure 12 The cycling performance of the lithium-sulfur battery in Example 1 of the present invention at 2 C was investigated. DETAILED DESCRIPTION

[0048] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0049] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments of the present invention. In the specific embodiments of the present invention, it is not mentioned that the temperature is room temperature.

[0050] Name and source of the drugs used in this invention:

[0051] Carbon black (KeQin 600, Materials Science Station), nitric acid (HNO3, Sinopharm Reagent), cobalt chloride (CoCl2, Sinopharm Reagent), triphenylphosphine (C 18 H 15 P, Sinopharm Reagent), 1,10-phenanthroline (C 12 All chemicals (H₂N₂, Sinopharm Reagent), cobalt acetate ((CH₃COO)₂Co, Sinopharm Reagent), and ethanol (C₂H₂O, Sinopharm Reagent) were of analytical grade and used without further purification. Ultrapure water (R = 18.25 MΩ) was used in all experiments.

[0052] In the present invention, the methods used for material characterization are:

[0053] The phase composition and surface chemistry of Co-NC-P, Co-NC, and NC-P were characterized by X-ray diffraction (XRD, Rigaku SmartLab, using a Cu Kα radiation source) and X-ray photoelectron spectroscopy (XPS, Thermo Escalab, using an Al Kα radiation source). Their structural and morphological properties were investigated using high-resolution field-emission transmission electron microscopy (HRTEM, JEOL ARM-200F) and field-emission scanning electron microscopy (FESEM, Zeiss Gemini 300). The Co content in Co-NC and Co-NC-P was determined using inductively coupled plasma spectrometry (ICP-MS, PerkinElmer 7300DV). Co K-edge near-edge X-ray absorption spectroscopy (XANES) and extended-edge X-ray absorption fine structure (EXAFS) spectra were measured at the BL14W1 beamline at the Shanghai Synchrotron Radiation Facility (SSRF). Athena software was used to calibrate the energy scale, correct the signal background, normalize the signal intensity, and transform the data from K space to R space. The first cycle of the Li-S battery (20°-30°, 5 °C min -1 ) were characterized by in situ XRD.

[0054] Experimental Example 1:

[0055] This embodiment discloses a Co single-atom catalyst coordinated by a second shell phosphorus atom and a preparation method thereof. The process is as follows: Figure 1 As shown, the specific preparation method includes the following steps:

[0056] (1) Place 0.045 g of cobalt acetate and 0.1 g of 1,10-phenanthroline in a test tube containing 10 mL of anhydrous ethanol solution and stir ultrasonically for 0.5 h to obtain a light yellow liquid, which is a solution of 1,10-phenanthroline molecules coordinated with cobalt metal ions.

[0057] (2) Preparation of oxygen-doped carbon CO:

[0058] 1 g of carbon black, 230 mL of concentrated HNO₃ (68 wt%), and 70 mL of H₂O were added to a 500 mL round-bottom flask and ultrasonically stirred for 0.5 h each to uniformly disperse the carbon black in the solution. The flask was then placed in a reflux system and heated for oxidation at 80 °C for 24 h. After the reaction was terminated and cooled to room temperature, the carbon black was washed with ultrapure water and ethanol by centrifugation until the pH of the washings reached neutral. The sample was then dried in a vacuum oven at 70 °C and designated as CO.

[0059] (3) Preparation of phosphorus-doped carbon CP:

[0060] 50 mg of CO obtained in (2) and 0.5 g of triphenylphosphine were placed in a round-bottom flask, and 20 mL of anhydrous ethanol was added and stirred with ultrasound until the triphenylphosphine was dissolved. The mixture was dried by rotary evaporation on a rotary evaporator until no liquid remained. The mixture was heated at 10 °C min under Ar / H2 (H2 concentration was 5% by volume) conditions. -1 The reaction was continued for 2 h at a heating rate of 100 ℃ to 750 °C to obtain CP.

[0061] (4) The 1,10-phenanthroline molecule coordinated cobalt metal ion solution and phosphorus-doped carbon CP were mixed evenly, dried by rotary evaporation, and calcined at high temperature to obtain the second shell phosphorus atom coordinated Co single atom catalyst Co-NC-P:

[0062] 50 mg of CP and 1 mL of the solution obtained by (1) were added to 5 mL of ethanol, and ultrasonically stirred for 0.5 h each. The reaction was carried out in a water bath at 60 °C for 4 h under well-dispersed conditions, and the precursor was obtained by rotary evaporation drying. Finally, the above precursor was heated in Ar at 5 °C min -1 The mixture was heated to 600 °C at a heating rate of 100 °C for 2 h and then naturally cooled to room temperature to obtain Co-NC-P.

[0063] The prepared Co-NC-P was analyzed by XRD, and the results are shown in Figure 2 The synthesized sample does not contain metallic Co phase. TEM analysis of the prepared Co-NC-P was performed. Figure 3It can be seen that the prepared Co-NC-P is carbon nanoparticles without aggregation of metal nanoparticles. The prepared Co-NC-P was characterized by HAADF. The HAADF-STEM image shows that the Co atoms in Co-NC-P appear as dispersed bright spots on the carbon substrate ( Figure 4 ), it can be seen that Co is dispersed on the carbon substrate in the form of atoms. The prepared Co-NC-P was characterized by elemental analysis, and the energy dispersive X-ray spectroscopy (EDX) diagram ( Figure 5 ) showed that N, Co and P were uniformly dispersed on the carbon substrate.

[0064] The chemical states of Co, N and P elements were then studied using X-ray photoelectron spectroscopy (XPS). Figure 6 As shown in Figure a, the deconvoluted N 1s XPS spectrum of Co-NC shows four peaks at binding energies of 398.69 eV, 399.44 eV, 400.6 eV, and 404.2 eV, corresponding to pyridinic N, pyrrolic N, graphitic N, and oxidized N, respectively. Compared with Co-NC, the peak of pyridinic N in Co-NC-P shifts toward lower energy, indicating that the introduction of P affects the electronic structure of pyridinic N. Co 2p XPS spectrum of Co-NC ( Figure 6 (b) shows Co 2p 3 / 2 and Co 2p 1 / 2 The binding energies of are 780.95 eV and 796.45 eV, respectively, and there are two satellite peaks. After binding with P atoms, Figure 6 As shown in Figure (c), the Co 2p peak in Co-NC-P exhibits a slight negative binding energy shift, located at 780.84 eV and 796.35 eV, respectively. This indicates that the chemical state of Co in Co-NC-P changes due to binding with P atoms, leading to an increase in electron density. Furthermore, the high-resolution P 2p XPS spectrum of Co-NC-P shifts to higher binding energies compared to CP, indicating a significant decrease in P electron density through electron transfer. Furthermore, the characteristic peaks of the Co-P bond are not detected in the P 2p spectrum of Co-NC-P, indicating that P atoms do not directly bind to Co atoms but rather remotely influence the state of Co atoms through binding with nitrogen.

[0065] X-ray absorption spectroscopy was further used to determine the electronic structure and coordination environment of the Co site. Figure 7As shown, the Fourier transformed spectra show that no Co-Co interaction peak (2.17 Å) is found in Co-NC and Co-NC-P, indicating that the Co atoms are in an atomically dispersed state in Co-NC and Co-NC-P. The peak at 1.35 Å for Co-NC and the peak at 1.44 Å for Co-NC-P are mainly attributed to the Co-N coordination of the first shell. It is worth noting that the slight shift of the Co-N peak between Co-NC and Co-NC-P may be due to the different Co-N coordination environment caused by the introduction of P atoms. The fitting results show that the atomically dispersed Co atoms are coordinated with 4 N atoms. The above results show that Co in Co-NC-P is coordinated with 4 N to form the first coordination shell, and P is introduced into the second coordination shell of the Co site.

[0066] Experimental Example 2:

[0067] This embodiment discloses a Co single-atom catalyst coordinated by a second-shell phosphorus atom and a preparation method thereof, the preparation method comprising the following steps:

[0068] (1) Place 0.045 g of cobalt acetate and 0.15 g of 1,10-phenanthroline in a test tube containing 10 mL of anhydrous ethanol solution and stir ultrasonically for 0.5 h to obtain a light yellow liquid, which is a solution of 1,10-phenanthroline molecules coordinated with cobalt metal ions.

[0069] (2) Preparation of oxygen-doped carbon CO:

[0070] 0.5 g of carbon black, 230 mL of concentrated HNO₃ (68 wt%), and 70 mL of H₂O were added to a 500 mL round-bottom flask and ultrasonically stirred for 0.5 h each time to uniformly disperse the carbon black in the solution. The flask was then placed in a reflux system and heated for oxidation at 80 °C for 24 h. After the reaction was terminated and cooled to room temperature, the carbon black was washed with ultrapure water and ethanol by centrifugation until the pH of the washings reached neutral. The sample was then dried in a vacuum oven at 70 °C and designated as CO.

[0071] (3) Preparation of phosphorus-doped carbon CP:

[0072] 50 mg of CO obtained in (2) and 250 mg of triphenylphosphine were placed in a round-bottom flask, 20 mL of anhydrous ethanol was added and ultrasonically stirred until the triphenylphosphine was dissolved, and the mixture was dried by rotary evaporation on a rotary evaporator. The mixture was heated at 10 °C min under Ar / H2 (H2 concentration was 5%). -1 The reaction was continued for 2 h at a heating rate of 100 °C to obtain CP.

[0073] (4) The solution of 1,10-phenanthroline molecules coordinated with cobalt metal ions was mixed evenly with phosphorus-doped carbon, dried by rotary evaporation, and calcined at high temperature to obtain the second shell phosphorus atom coordinated Co single atom catalyst Co-NC-P:

[0074] 75 mg of CP and 1 mL of the solution obtained by (1) were added to 5 mL of anhydrous ethanol, and ultrasonically stirred for 0.5 h each. The reaction was carried out in a water bath at 60 °C for 4 h under well-dispersed conditions, and the precursor was obtained by rotary evaporation drying. Finally, the above precursor was heated in Ar at 4 °C min -1 The mixture was heated to 500 °C at a heating rate of 1.5 h and then cooled naturally to room temperature to obtain Co-NC-P.

[0075] Experimental Example 3:

[0076] This embodiment discloses a Co single-atom catalyst coordinated by a second-shell phosphorus atom and a preparation method thereof, the preparation method comprising the following steps:

[0077] (1) Place 0.045 g of cobalt acetate and 0.25 g of 1,10-phenanthroline in a test tube containing 10 mL of anhydrous ethanol solution and stir ultrasonically for 0.5 h to obtain a light yellow liquid, which is a solution of 1,10-phenanthroline molecules coordinated with cobalt metal ions.

[0078] (2) Preparation of oxygen-doped carbon CO:

[0079] 2 g of carbon black, 230 mL of concentrated HNO₃ (68 wt%), and 70 mL of H₂O were added to a 500 mL round-bottom flask and ultrasonically stirred for 0.5 h each to uniformly disperse the carbon black in the solution. The flask was then placed in a reflux system and heated for oxidation at 80 °C for 24 h. After the reaction was terminated and cooled to room temperature, the carbon black was washed with ultrapure water and ethanol by centrifugation until the pH of the washings reached neutral. The sample was then dried in a vacuum oven at 70 °C and recorded as CO.

[0080] (3) Preparation of phosphorus-doped carbon CP:

[0081] 50 mg of CO obtained in (2) and 1 g of triphenylphosphine were placed in a round-bottom flask, and 20 mL of anhydrous ethanol was added and stirred with ultrasonic waves until the triphenylphosphine was dissolved. The mixture was dried by rotary evaporation on a rotary evaporator and heated at 10 °C min under Ar / H2 (H2 concentration was 5%). -1 The mixture was heated to 800 °C at a heating rate of 100 °C and reacted for 2 h to obtain CP.

[0082] (4) The solution of 1,10-phenanthroline molecules coordinated with cobalt metal ions was mixed evenly with phosphorus-doped carbon, dried by rotary evaporation, and calcined at high temperature to obtain the second shell phosphorus atom coordinated Co single atom catalyst Co-NC-P:

[0083] 100 mg of CP and 2 mL of the solution obtained by (1) were added to 5 mL of anhydrous ethanol, and ultrasonically stirred for 0.5 h each. The reaction was carried out in a water bath for 4 h under well-dispersed conditions, and the precursor was obtained by rotary evaporation drying. Finally, the above precursor was heated in Ar at 8 °C min -1 The mixture was heated to 900 °C at a heating rate of 100 °C for 2 h and then naturally cooled to room temperature to obtain Co-NC-P.

[0084] Experimental Example 4:

[0085] This comparative example provides the preparation of a phosphorus-free Co catalyst Co-NC, specifically:

[0086] 0.1 g of 1,10-phenanthroline and 0.045 g of cobalt chloride were dissolved in 10 ml of ethanol to form a solution (Co solution). 50 mg of carbon black and 1 ml of Co solution were added to 5 ml of ethanol and ultrasonically stirred for 0.5 h each. The mixture was reacted in a water bath for 4 h under well-dispersed conditions and then dried by rotary evaporation. Finally, the precursor was heated in Ar at 5 °C min -1 The samples were heated to 600 °C at a heating rate of 100 °C and annealed for 2 h to obtain Co-NC.

[0087] Experimental Example 5:

[0088] This embodiment provides the preparation of a cobalt-free P-doped C catalyst CP, specifically the following steps: 1 g of carbon black, 230 mL of concentrated HNO3 (68 wt%), and 70 mL of H2O were added to a 500 mL round-bottom flask, ultrasonically stirred for 0.5 h each to uniformly disperse the carbon black in the solution, and then the flask was placed in a condensing reflux system and heated and oxidized at 80 °C for 24 h. After the reaction was stopped, the carbon black cooled to room temperature was washed with ultrapure water and ethanol and centrifuged until the pH of the washing liquid reached neutral. The sample was then dried in a vacuum oven at 70 °C, and the resulting sample was recorded as CO. 50 mg of CO and 1 g of triphenylphosphine were placed in a round-bottom flask, 20 mL of anhydrous ethanol was added and ultrasonically stirred until the triphenylphosphine was dissolved, and the mixture was dried by rotary vaporization on a rotary evaporator, and the mixture was dried under Ar / H2 conditions at 10 °C min -1 The mixture was heated to 800 °C at a heating rate of 100 °C and reacted for 2 h to obtain CP.

[0089] Example 1:

[0090] This embodiment provides the application of the catalytic materials obtained in Experimental Examples 1, 4, and 5 above in battery components and battery preparation, including:

[0091] (1) Preparation of modified diaphragms for lithium-sulfur batteries: The prepared catalytic materials (Co-NC-P in Experimental Example 1, Co-NC in Experimental Example 4, and CP in Experimental Example 5), acetylene black, and PVDF were dispersed in NMP at a mass ratio of 7:2:1. The mixture was placed in a planetary ball mill and fully mixed for 3 h. The mixed slurry was cast on a Celgard 2400 diaphragm and evenly coated with a 50 μm thick scraper. The diaphragm was placed in a vacuum oven at 60 °C and dried for 12 h to prepare a diaphragm with a diameter of 19 mm and a thickness of 10 μm.

[0092] (2) Electrode preparation: Co-NC-P, Co-NC, CP and PVDF binder were mixed in NMP at a weight ratio of 9:1, coated on aluminum foil as electrode material, and dried in a vacuum oven at 60 °C for 12 h to prepare an electrode with a diameter of 12 mm and a catalyst loading of 1.5 mg cm -2 .

[0093] (3) Adsorption test of modified electrolyte: The effective adsorption of LiPSs by catalytic materials can improve the utilization rate of sulfur active substances. In order to compare the adsorption performance of different catalytic materials on LiPSs, a visual Li2S6 adsorption performance test was carried out. The same mass of Co-NC-P, Co-NC and CP materials were dispersed in the same volume of Li2S6 electrolyte. Figure 8 As shown, the Li2S6 electrolyte without any added catalytic material appears yellow. The color of the Li2S6 solution containing Co-NC-P almost fades after 6 hours. In contrast, the Co-NC solution shows slight discoloration after 6 hours, demonstrating weak adsorption of Li2S6 by Co-NC. Even after 6 hours, no significant discoloration is observed for the CP solution, demonstrating the strong adsorption capacity of Co-NC-P for Li2S6.

[0094] (4) Lithium-sulfur battery: The electrochemical performance of Li-S battery was evaluated using a button cell (CR2016) with S@C electrode as the positive electrode, lithium metal as the negative electrode, and Celgard 2400 membrane modified with catalytic material as the separator.

[0095] The cycling performance of the battery was tested using a Neware battery testing system (CT-4008, Shenzhen, China) in the voltage range of 1.7 to 2.8 V. CV tests at different scan rates were performed on the battery using a CHI 760E electrochemical workstation in the voltage range of 1.7 to 2.8 V.

[0096] Among them, the electrode preparation: sulfur powder and carbon black are mixed uniformly by ball milling at a mass ratio of 7:3 to obtain a carbon black / S mixture. The mixture is then placed in an ampoule and the sulfur-carbon composite material is prepared by a conventional molten sulfur impregnation method. -1 The temperature was heated to 155 °C and held for 12 h to allow the S element to melt and diffuse into the carbon black. -1 The temperature was raised to 185 °C at a rate of 100 °C and held for 2 h to volatilize the S floating on the surface, thereby obtaining the final carbon black@S. The prepared carbon black@S, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1 and then uniformly dispersed in N-methylpyrrolidone (NMP) to obtain a slurry. The slurry was evenly coated on an aluminum foil using a coater. The prepared sulfur cathode film had a thickness of 200 µm and was placed in a vacuum oven at 60 °C and dried for 12 h to prepare a S@C electrode with a diameter of 12 mm and a sulfur loading of approximately 1.5 mg cm -2 .

[0097] (5) Soft-pack battery: The electrode is made of carbon black@S with a sulfur loading of 80%, carbon black and PVDF in a mass ratio of 8:1:1, and then stirred in NMP for 12 h to obtain a uniformly dispersed slurry. The sulfur positive electrode coating is prepared with a coater to a thickness of 750 μm, and is placed in a vacuum oven at 60 °C and dried for 12 h to prepare a 9×6 cm soft-pack electrode with a 1×1 cm tab reserved. The sulfur loading is approximately 6.94 mg cm -2 The negative electrode is a 100 µm-thick lithium ribbon measuring 9 x 6 cm. The separator is modified with the aforementioned catalyst. Aluminum and nickel tabs are used to weld the positive and negative electrodes, respectively. The aluminum-plastic film is 100 µm thick and has a 4 mm crater depth. The pouch cell assembly uses two single-sided coated and three double-sided coated positive electrodes, with a total sulfur loading of 3 g. Eight lithium sheets serve as the negative electrode, and the total electrolyte volume is 8.1 mL.

[0098] The lithium-sulfur batteries prepared using Co-NC-P and samples without Co (CP) or phosphorus (Co-NC) in (4) were tested and characterized.

[0099] Figure 9 The cyclic voltammetry curves show two reduction peaks and one oxidation peak. The peak 1 at 2.3 V corresponds to the conversion of solid S8 to long-chain Li2S xPeak 2, located near 2.0 V, corresponds to the reduction of soluble Li2S4 to solid Li2S2 / Li2S. Peak 3, located at 2.1 V, is associated with the conversion of Li2S2 / Li2S to S8. Clearly, compared to Co-NC and CP, the reduction peak of Co-NC-P exhibits a higher peak potential and a higher current response, while the oxidation peak exhibits a lower peak potential and a higher current response, demonstrating that Co-NC-P has a lower polarization voltage and higher catalytic performance, improving redox reaction kinetics and promoting the electrochemical reaction.

[0100] In order to explore the effect of catalysis on the electrochemical performance of lithium-sulfur batteries, separators modified with Co-NC-P, Co-NC and CP catalysts were prepared to assemble button cells. Figure 10 As shown, compared with Co-NC and (1113, 1035, 956, 897, 841, 776 and 705 mAhg -1 )CP (973, 913, 845, 836, 788, 729 and 630 mAhg -1 ) compared to the Co-NC-P batteries, which showed higher specific capacities (1213, 1141, 1065, 1008, 960, 903, and 831 mAhg) in the current density range of 0.5 to 6 C. -1 ). It can be seen that the rate performance of the lithium-sulfur battery assembled with Co-NC-P modified separator is 831 mAh g at 6C rate. -1 The specific capacity of Co-NC-P shows that it has good performance at high current density.

[0101] The cycling performance of the assembled lithium-sulfur battery at 0.5 C is shown in Figure 11 As shown in Figure 2, after 200 cycles at a current density of 0.5 C, the specific capacity of the Co-NC-P battery still remains at 963 mAhg -1 , which is higher than that of Co-NC and CP (705 mAh g -1 and 643 mAh g -1 ), indicating that the excellent catalytic activity of Co-NC-P improves the cycling reversibility of the battery.

[0102] Long-term cycling stability testing with high capacity retention is an important indicator for the industrial application of LSBs. First, the discharge curves of Co-NC-P, Co-NC, and CP were compared after 150 cycles at a current density of 2 C. The discharge curve of Co-NC-P still maintained two complete reaction platforms at 150 cycles, and the capacity retention rate was as high as 92.6%. In contrast, the capacity retention rates of Co-NC and CP were 88.9% and 83.8%, respectively. The second discharge reaction platform gradually deviated from the original platform, indicating that the interaction with LiPSs was weaker, resulting in a larger polarization reaction. Figure 12 It is shown that after 1500 cycles at a current density of 2 C, the Co-NC-P based battery still achieves 511 mA h g -1 The specific capacity of Co-NC-P is 0.034% per cycle, and the average cycle decay rate is 0.034%. The excellent cycling stability can be attributed to the proper combination of Co-NC-P and LiPSs, which can effectively inhibit the LiPSs shuttle effect and accelerate the desorption of Li2S to improve the reaction kinetics.

[0103] The above fully demonstrates that the Co-NC-P catalytic material prepared by the present invention can optimize the adsorption of polysulfides and promote the rapid conversion of polysulfides; it can effectively improve the shuttle effect of lithium-sulfur batteries, thereby improving key electrochemical indicators such as battery performance and cycle stability.

[0104] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A modified separator for a lithium-sulfur battery, characterized in that: The lithium-sulfur battery modified diaphragm is modified with a second shell phosphorus atom coordinated Co single atom catalyst; The preparation method of the second shell phosphorus atom coordinated Co single atom catalyst comprises the following steps: S1. preparing a solution of 1,10-phenanthroline molecules coordinated with cobalt metal ions; S2, preparing phosphorus-doped carbon; S3. The solution of 1,10-phenanthroline molecules coordinated with cobalt metal ions is evenly mixed with phosphorus-doped carbon, dried by rotary evaporation, and calcined at high temperature to obtain a second-shell phosphorus atom coordinated Co single-atom catalyst.

2. A modified separator for lithium-sulfur batteries according to claim 1, characterized in that: In step S1, the concentration of the cobalt metal ion solution is 0.01-0.04 mol / L, and the molar concentration ratio of 1,10-phenanthroline to cobalt metal is 2-5:

1.

3. A modified separator for lithium-sulfur batteries according to claim 1, characterized in that: In step S1, the cobalt metal is selected from at least one of cobalt acetate, cobalt acetate tetrahydrate, cobalt nitrate, cobalt carbonate and cobalt chloride.

4. A modified separator for lithium-sulfur batteries according to claim 1, characterized in that: In step S2, oxygen-doped carbon and triphenylphosphine are mixed, calcined at high temperature in an argon-hydrogen atmosphere, and cooled to room temperature to prepare phosphorus-doped carbon; The mass ratio of the oxygen-doped carbon to triphenylphosphine is 1:5, 1:10 or 1:

20.

5. A modified separator for lithium-sulfur batteries according to claim 4, characterized in that: The high temperature calcination condition in the argon-hydrogen atmosphere is 8-12 ° C min -1 The temperature is heated to 600-800°C at a rate of 10000°C for 1-4 hours and then cooled to room temperature naturally to obtain phosphorus-doped carbon.

6. A modified separator for lithium-sulfur batteries according to claim 4, characterized in that: The preparation method of the oxygen-doped carbon is as follows: carbon black is oxidized with nitric acid at 70-90° C. in a reflux system for 20-28 hours, cooled to room temperature, washed with ultrapure water and ethanol until the pH value of the solution reaches neutral, and then dried in a vacuum oven at 60-90° C.

7. A modified separator for lithium-sulfur batteries according to claim 6, characterized in that: The amount of carbon black is 0.5~2 g, and the concentration of nitric acid is 12 M.

8. A modified separator for lithium-sulfur batteries according to claim 1, characterized in that: In step S3, 0.5-2 mL of 1,10-phenanthroline molecule coordinated cobalt metal ion solution and 50-100 mg of phosphorus-doped carbon are dispersed in 2.5-7.5 mL of anhydrous ethanol, mixed evenly, and then dried by rotary evaporation and calcined at high temperature to obtain a second shell phosphorus atom coordinated Co single atom catalyst.

9. A modified separator for lithium-sulfur batteries according to claim 8, characterized in that: The high-temperature calcination conditions are as follows: in an argon atmosphere, heating at a rate of 4-8°C / min to 500-900°C, continuously heating for 1.5-2 hours, and naturally cooling to room temperature.

10. The method for preparing a modified lithium-sulfur battery separator according to any one of claims 1 to 9, characterized in that: The second shell phosphorus atom coordinated Co single atom catalyst, acetylene black, and polyvinylidene fluoride were dispersed in N-methylpyrrolidone at a mass ratio of 7:2:1 and mixed thoroughly to obtain a slurry. The slurry was evenly coated on the diaphragm and dried in a vacuum oven at 60°C for 12 h. The membrane included Celgard 2400 membrane.

11. Use of the modified lithium-sulfur battery separator according to any one of claims 1 to 9 in the preparation of lithium-sulfur batteries or soft-pack batteries.

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