Ionic liquid assisted synthesized Fe-N-C monatomic catalyst material and preparation method thereof
By synthesizing Fe-NC single-atom catalyst materials with ionic liquid assistance, the problem of polysulfide shuttle effect in lithium-sulfur batteries was solved, the cycle stability and discharge capacity of lithium-sulfur batteries were improved, the redox kinetics were improved, and high-performance lithium-sulfur batteries were realized.
Patent Information
- Application Number
- CN202411015920.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-26
- Publication Date
- 2026-01-27
AI Technical Summary
Lithium-sulfur batteries suffer from lithium dendrites, lithium sulfide passivation layers, and severe polysulfide shuttle effects, leading to rapid capacity decay. Existing composite sulfur cathode designs are complex and have limited applications.
Fe-NC single-atom catalyst materials were synthesized using ionic liquid-assisted synthesis. The process involved SiO2 nanosphere template preparation, Fe3+-PDA@SiO2 nanosphere formation, carbonization, and post-treatment to prepare Fe-NC single-atom catalysts. These catalysts were then applied to the modification of lithium-sulfur battery separators, introducing N, O, and P heteroatoms to increase the surface defect density of carbon nanospheres and form a metal single-atom and nitrogen-doped carbon framework.
It significantly suppresses the shuttle effect, improves the utilization rate of active materials, enhances the cycle stability and discharge capacity of lithium-sulfur batteries, improves redox kinetics, and realizes high-performance lithium-sulfur batteries.
Smart Images
Figure CN121402111A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrochemical technology of new energy materials, and relates to an ionic liquid-assisted synthesis of Fe-NC single-atom catalyst material, its preparation method, and its application in lithium-sulfur battery separators. Background Technology
[0002] With the continuous development of science and technology, the demand for high-energy-density battery systems has increased dramatically. Therefore, developing a new generation of inexpensive and efficient batteries has become urgent. Among these, lithium-sulfur batteries, which use elemental sulfur or sulfur-containing compounds as the positive electrode, have a high energy density of 2600 Wh / kg. -1 Theoretical energy density and 1675 mAh g -1 Sulfur has attracted much attention due to its theoretical specific capacity. At the same time, sulfur has advantages such as low price, abundant reserves, and environmental friendliness, making it suitable for the current needs of new energy vehicles and large-scale energy storage.
[0003] Although lithium-sulfur batteries have significant advantages in terms of specific energy and cost, some key issues still need to be addressed, including lithium dendrites, lithium sulfide passivation layers, and a severe "shuttle effect." The severe shuttle effect and slow reaction kinetics of polysulfides (LPS) are the main reasons for the rapid capacity decay of lithium-sulfur batteries.
[0004] To address the aforementioned issues, researchers have primarily improved the electrochemical performance of lithium-sulfur batteries by designing composite sulfur cathodes. However, the design and fabrication processes of composite sulfur cathodes are complex, and their practical applications face certain limitations. Researchers have proposed that functional modification of the separator is a simple and effective method. Summary of the Invention
[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing Fe-NC single-atom catalyst materials using ionic liquid-assisted synthesis.
[0006] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing Fe-NC single-atom catalyst materials assisted by ionic liquid synthesis, comprising the following steps:
[0007] Step 1: Preparation of SiO2 nanosphere template: Tetraethoxysilane was added dropwise to a mixed solution of ethanol, concentrated ammonia solution and distilled water under stirring at room temperature. After stirring, SiO2 nanospheres were collected by centrifugation and washed with distilled water and ethanol. The collected nanospheres were then dried and the dried white powder was ground for later use.
[0008] Step 2: Fe 3+ Preparation of PDA@SiO2 nanospheres: Dopamine monomer and Fe3+ The solution chelates with the aid of 1-hexyl-3-methylimidazolium hexafluorophosphate ionic liquid and self-polymerizes on SiO2 nanospheres in a weakly alkaline solution to form a core-shell Fe. 3+ -PDA@SiO2 nanospheres;
[0009] Step 3: Carbonization: The Fe obtained in Step 2... 3+ - PDA@SiO2 nanospheres were calcined and cooled to obtain carbon-encapsulated silica nanospheres with Fe metal single atoms dispersed.
[0010] Step 4: Post-processing: The SiO2 template is etched with a high-concentration NaOH solution and then subjected to a second high-temperature calcination to obtain the Fe-NC single-atom catalyst material synthesized with ionic liquid assistance.
[0011] Preferably, in step one, the amount of tetraethoxysilane is 2.7 mL; the amount of ethanol is 180 mL; the amount of concentrated ammonia is 30 mL; and the amount of distilled water is 9 mL; the stirring time in step one is 24 h; the centrifugation speed is 6000–8000 r / min; the centrifugation time is 2–5 min; the drying temperature is 50–70 °C; the drying time is 12–24 h; and the concentration of the concentrated ammonia solution is 25–28%.
[0012] Preferably, the Fe in step two 3+ The solution is Fe(NO3)3·9H2O, and the weakly alkaline solution is tris(hydroxymethyl)aminomethane.
[0013] Preferably, the atmosphere during calcination in step three is a nitrogen atmosphere, the calcination temperature is 950℃, the calcination time is 3h, and the heating rate is 5℃ / min.
[0014] Preferably, in step four, the NaOH concentration is 5 mol / L, the soaking time is 24 h, and the temperature is 60 °C.
[0015] The present invention also provides an ionic liquid-assisted synthesis of Fe-NC single-atom catalyst material prepared according to the above preparation method.
[0016] The present invention also provides a modified membrane, the modified membrane comprising: a membrane, and a modification layer formed on the surface of the membrane, wherein the modification layer is made of the aforementioned ionic liquid-assisted synthesis Fe-NC single-atom catalyst material. Preferably, the thickness of the modification layer is 25–40 μm; the modification layer further comprises a binder and a conductive agent; the binder is polyvinylidene fluoride; the conductive agent is conductive carbon black; the mass ratio of the Fe-NC single-atom catalyst material, the binder, and the conductive agent is 8:1:1.
[0017] The present invention also provides a lithium-sulfur battery, comprising: a sulfur-carbon positive electrode; the modified separator described above; a lithium negative electrode; and an electrolyte. Preferably, the lithium-sulfur battery is assembled in the following order to form a button cell: positive electrode shell, sulfur-carbon positive electrode, electrolyte, modified separator, electrolyte, lithium negative electrode, steel sheet, spring sheet, and negative electrode shell.
[0018] Compared with existing preparation methods, this invention utilizes an ionic liquid (1-hexyl-3-methylimidazolium hexafluorophosphate) to assist in the synthesis of Fe-NC / HSs. Ionic liquid doping not only introduces heteroatoms such as N, O, and P, but also effectively increases the defect density of carbon nanospheres, significantly expanding their outer surface area and allowing for higher metal atom doping. Subsequently, high-temperature pyrolysis forms metal single atoms and a nitrogen-doped carbon framework. The monodisperse metal atoms exhibit very high catalytic activity towards polysulfides, efficiently utilizing polysulfides dissolved from the cathode, greatly improving the utilization rate of active materials, and significantly suppressing the shuttle effect, thus achieving a high-performance lithium-sulfur battery. Furthermore, the Fe-NC / HSs prepared in this invention, when used for lithium-sulfur battery separator modification, exhibits a significant catalytic conversion effect on polysulfides generated in the lithium-sulfur battery. At 0.2C, the initial charge-discharge specific capacity of the lithium-sulfur battery reaches 1400 mAh / g, demonstrating high discharge capacity and excellent cycle stability and rate performance; both the initial discharge specific capacity and capacity retention are higher than the comparative example. Regarding battery impedance data, the lithium-sulfur batteries prepared using the Fe-NC / HSs modified separator of this invention all exhibited lower impedances than the comparative examples. Furthermore, in redox kinetic testing, the lithium-sulfur batteries corresponding to the examples showed the smallest peak potential difference in the CV curve, indicating a significant improvement in redox kinetics. Attached Figure Description
[0019] Figure 1 These are SEM images of the NFP-FeNC / HSs and FeNC / HSs materials of this invention.
[0020] Figure 2 These are the cyclic voltammograms of lithium-sulfur batteries from Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention.
[0021] Figure 3 These are the impedance diagrams of lithium-sulfur batteries corresponding to Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention.
[0022] Figure 4 These are the 0.2C cycle performance diagrams of lithium-sulfur batteries corresponding to Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention. Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0024] Single-atom catalysts (SACs) are catalysts in which active atoms are isolated one by one using a matrix support material. When single-atom catalysts are used for membrane modification, they not only facilitate the adsorption of lithium polysulfides, but also bind to S, weakening the S-S bonds in chain-like lithium polysulfides, thereby promoting the decomposition of LPS or Li2S and facilitating redox reactions during charge and discharge processes.
[0025] Ionic liquids (ILs), composed of organic cations and inorganic anions, offer advantages such as low cost, eco-friendliness, abundance of heteroatoms, good solubility, and the ability to coordinate with metal ions, making them suitable precursors for catalyst preparation. In the preparation of single-atom MNC catalysts using ionic liquids (ILs), firstly, ILs can serve as heteroatom sources, providing elements such as nitrogen, phosphorus, and boron. These heteroatoms with lone pairs of electrons possess strong coordination capabilities and can anchor metal single atoms. Secondly, the incorporation of pyridine nitrogen and pyrrole nitrogen derived from ionic liquids can increase the defect density of carbon materials, providing strong anchoring sites for LPS, thereby effectively mitigating the shuttle effect.
[0026] To address the severe "shuttle effect" and other problems existing in lithium-sulfur batteries, this invention proposes an ionic liquid-assisted synthesis of Fe-NC single-atom catalyst materials, its preparation method, and its application in lithium-sulfur battery separators. This invention synthesizes Fe-NC / HSs using ionic liquid assistance and applies it to the modification of lithium-sulfur battery separators. The introduced metal single-atom catalyst can effectively alleviate the "shuttle effect" in lithium-sulfur batteries, promote the conversion of polysulfides, improve the utilization rate of active materials, and enhance the cycle performance and stability of the battery.
[0027] In a first aspect, the present invention provides a method for preparing Fe-NC single-atom catalyst materials using ionic liquid-assisted synthesis, comprising the following steps:
[0028] (1) Preparation of SiO2 nanosphere template: Tetraethoxysilane (TEOS) was added dropwise to a mixed solution of ethanol, concentrated ammonia solution and distilled water under magnetic stirring at room temperature; after additional stirring, SiO2 nanospheres were collected by centrifugation and washed three times with distilled water and ethanol. The collected SiO2 nanospheres were then dried overnight in a vacuum drying oven, and the dried white powder was ground for further use;
[0029] (2)Fe 3+ Preparation of PDA@SiO2 nanospheres: dopamine monomer and a certain amount of Fe3+ The solution chelates with the aid of 1-hexyl-3-methylimidazolium hexafluorophosphate ionic liquid and self-polymerizes on SiO2 nanospheres in a weakly alkaline solution to form a core-shell Fe. 3+ -PDA@SiO2 nanospheres;
[0030] (3) Carbonization: The Fe obtained in step (2) 3+ - PDA@SiO2 nanospheres were calcined and cooled to obtain carbon-encapsulated silica nanospheres with Fe metal single atoms dispersed, namely Fe-NC@SiO2 nanospheres;
[0031] (4) Post-processing: Etching the SiO2 template with high-concentration NaOH solution and performing secondary high-temperature calcination can yield a unique ionic liquid-assisted synthesis of Fe-NC single-atom catalyst material (i.e., Fe-NC@SiO2 nanospheres).
[0032] In step (1), the amount of TEOS is 2.7 mL; the amount of ethanol is 180 mL, the volume is 30 mL, and the amount of distilled water is 9 mL; the stirring time in step (1) is 24 h. In step (1), the centrifugation speed is 6000–8000 r / min, and the time is 2–5 min; the drying temperature is 50–70 °C, and the time is 12–24 h. In step (1), the concentration of the concentrated ammonia solution is 25–28%.
[0033] In step (2), SiO2 is 2g, dopamine hydrochloride is 0.625g, and Fe... 3+ The solution was 0.2 mmol Fe(NO3)3·9H2O, the weakly alkaline solution was 0.24 g Tris(hydroxymethyl)aminomethane (Tris), and the added 1-hexyl-3-methylimidazolium hexafluorophosphate ionic liquid accounted for 2.5% of the volume of the mixed solution; the stirring temperature was 25℃, and the stirring time was 24 h; the centrifugation speed in step (2) was 6000~8000 r / min, and the time was 2~5 min; the drying temperature was 50~70℃, and the time was 12~24 h.
[0034] In step (3), the atmosphere during roasting is nitrogen, the roasting temperature is 950℃, the roasting time is 3h, and the heating rate is 5℃ / min.
[0035] In step (4), the NaOH concentration is 5 mol / L (M), the soaking time is 24 h, and the temperature is 60 °C.
[0036] Secondly, the present invention provides a modified membrane, the modified membrane comprising: a membrane, and a modification layer formed on the surface of the membrane for the ionic liquid-assisted synthesis of Fe-NC single-atom catalyst material; the thickness of the modification layer is 25-40 μm; the composition of the modification layer further comprises a binder and a conductive agent; the binder is PVDF (polyvinylidene fluoride); the conductive agent is conductive carbon black (Super-P); the mass ratio of the ionic liquid-assisted synthesis of Fe-NC single-atom catalyst material, binder, and conductive agent is 8:1:1.
[0037] The modified membrane is prepared by vacuum filtration of a slurry containing a single-atom catalyst material, binder, and conductive agent for the ionic liquid-assisted synthesis of Fe-NC into a PP (Celgard 2500) membrane.
[0038] Thirdly, the present invention provides a lithium-sulfur battery, comprising: a sulfur-carbon positive electrode; a modified separator; a lithium negative electrode; and an electrolyte. The lithium-sulfur battery is assembled in the following order to form a button cell: positive electrode shell, sulfur-carbon positive electrode, electrolyte, modified separator, electrolyte, lithium negative electrode, steel sheet, spring sheet, and negative electrode shell.
[0039] Example 1:
[0040] A method for preparing NFP-FeNC / HSs, the steps of which are as follows:
[0041] Step 1: Synthesis of SiO2 Nanospheres
[0042] Under magnetic stirring at room temperature, 2.7 mL of tetraethoxysilane (TEOS) was added dropwise to a mixture of ethanol (180 mL), concentrated ammonia solution (30 mL), and distilled water (9 mL). After an additional 5 hours of stirring, SiO2 nanospheres were collected by centrifugation (8000 rpm, 3 min) and washed three times with distilled water and ethanol. The collected nanospheres were then dried overnight at 40 °C in a vacuum drying oven, and the dried white powder was ground for further use.
[0043] Step 2: Fe 3+ Preparation of PDA@SiO2 nanospheres
[0044] 2 g SiO2 was dispersed in 200 mL of deionized water and sonicated for 2 h. Then, 0.625 g dopamine hydrochloride, 0.2 mmol Fe(NO3)3·9H2O, and 3 mL of ionic liquid (1-hexyl-3-methylimidazolium hexafluorophosphate) were added to the solution to form a metal complex. After 15 min, 0.24 g tris(hydroxymethyl)aminomethane (Tris) was added to the solution to initiate the polymerization of dopamine. After stirring continuously at room temperature for 24 h, the black precipitate was collected by centrifugation and washed three times with water and ethanol to obtain Fe.3+ -PDA@SiO2 nanospheres.
[0045] Step 3: Synthesis of Fe-NC@SiO2 Nanospheres
[0046] The synthesized Fe 3+ - The PDA@SiO2 precursor was placed in a tube furnace and heated to 950°C under N2 flow at a heating rate of 5°C / min. -1 Pyrolysis for 3 hours.
[0047] Step 4: Post-processing
[0048] The obtained Fe-NC@SiO2 nanosphere sample was immersed in 5 mol / L NaOH for 48 hours to remove the SiO2 template, followed by washing with deionized water multiple times until the pH reached neutral, and then drying in a vacuum oven at 60°C overnight. Finally, NFP-FeNC / HSs were obtained.
[0049] Step 5: Diaphragm Preparation
[0050] The PFB-FeNC / HSs modified membrane was prepared by a simple vacuum filtration method. 70 wt% PFB-FeNC / HSs, 20 wt% PVDF, and 10 wt% conductive carbon black (Super-P) were mixed in N-methyl-2-pyrrolidone (NMP) solvent and ultrasonically dispersed for 2 h. Then, standard vacuum filtration was performed using a commercially available polypropylene (PP, Celgard 2500) membrane as the filter. Finally, the modified membrane was dried under vacuum at 60 °C for 12 h. The coating quality was controlled at 0.47 mg / cm³. 2 The coating thickness is controlled between 25 and 40 μm.
[0051] Step 6: Preparation of sulfur-carbon cathode
[0052] Sulfur-carbon composite material was prepared as the cathode active material via melt diffusion (155℃, 12h), with a sulfur to multi-walled carbon nanotubes (MWCNTs) mass ratio of 3:1 (named S@MWCNTs). The obtained sulfur-carbon composite material, conductive carbon black (Super-P), and PVDF were mixed at a mass ratio of 8:1:1 using NMP as a solvent and homogenized by hand milling. The slurry was then coated onto carbon-coated aluminum foil using a doctor blade with a blade height of 150 μm. The electrode was then dried in a vacuum oven at 50℃ for 12h. The resulting lithium-sulfur battery cathode electrode had a sulfur loading of approximately 1.0-1.5 mg / cm³. 2 .
[0053] Step 7: Battery fabrication
[0054] In a glove box, a button cell is assembled in the following order: positive electrode shell, sulfur-carbon positive electrode, electrolyte, modified separator, electrolyte, lithium negative electrode, steel sheet, spring sheet, and negative electrode shell (the contents of O2 and H2O are both less than 0.01ppm).
[0055] Example 2:
[0056] A method for preparing NFP-Fe-NC / HSs, the steps of which are as follows:
[0057] Step 1: Synthesis of SiO2 Nanospheres
[0058] TEOS (2.7 mL) was added dropwise to a mixture of ethanol (180 mL), concentrated ammonia solution (30 mL), and distilled water (9 mL) under magnetic stirring at room temperature. After an additional 5 hours of stirring, SiO2 nanospheres were collected by centrifugation (8000 rpm, 3 min) and washed three times with distilled water and ethanol. The collected nanospheres were then dried overnight at 40 °C in a vacuum drying oven, and the dried white powder was ground for further use.
[0059] Step 2: Fe 3+ Preparation of PDA@SiO2 nanospheres
[0060] 2 g SiO2 was dispersed in 200 ml deionized water and sonicated for 2 h. Then, 0.625 g dopamine hydrochloride, 0.04 mmol Fe(NO3)3·9H2O, and 1 mL of ionic liquid (1-hexyl-3-methylimidazolium hexafluorophosphate) were added to the solution to form a metal complex. After 15 minutes, 0.24 g Tris was added to the solution to initiate the polymerization of dopamine. After stirring continuously at room temperature for 24 h, the black precipitate was collected by centrifugation and washed three times with water and ethanol to obtain Fe. 3+ -PDA@SiO2 nanospheres.
[0061] Step 3: Synthesis of Fe-NC@SiO2 Nanospheres
[0062] The synthesized Fe 3+ - The PDA@SiO2 precursor was placed in a tube furnace and heated to 950°C under N2 flow at a heating rate of 5°C / min. -1 Pyrolysis for 3 hours.
[0063] Step 4: Post-processing
[0064] The obtained Fe-NC@SiO2 nanosphere sample was immersed in 5 mol / L NaOH for 48 hours to remove the SiO2 template, followed by washing with deionized water multiple times until the pH reached neutral, and then drying in a vacuum oven at 60°C overnight. Finally, Fe-NC / HSs was obtained.
[0065] Step 5: Diaphragm Preparation
[0066] The NiFe@NC modified membrane was prepared by a simple vacuum filtration method. 70 wt% NiFe@NC, 20 wt% PVDF, and 10 wt% Super-P were mixed in N-methyl-2-pyrrolidone (NMP) solvent and ultrasonically dispersed for 2 h. Then, standard vacuum filtration was performed using a commercially available polypropylene (PP, Celgard 2500) membrane as the filter. Finally, the modified membrane was dried under vacuum at 60 °C for 12 h. The coating quality was controlled at 0.47 mg / cm³. 2 The coating thickness is controlled between 25 and 40 μm.
[0067] Step Six: Preparation of Sulfur-Carbon Cathode
[0068] Sulfur-carbon composite material was prepared as the cathode active material via melt diffusion (155℃, 12h), with a sulfur to MWCNTs mass ratio of 3:1 (named S@MWCNTs). The obtained sulfur-carbon composite material, Super-P, and PVDF were mixed at a mass ratio of 8:1:1 using NMP as a solvent and homogenized by hand milling. The slurry was then coated onto carbon-coated aluminum foil using a doctor blade with a blade height of 150 μm. The electrode was then dried in a vacuum oven at 50℃ for 12h. The resulting lithium-sulfur battery cathode electrode had a sulfur loading of approximately 1.0-1.5 mg / cm³. 2 .
[0069] Step 7: Battery fabrication
[0070] In a glove box, a button cell is assembled in the following order: positive electrode shell, sulfur-carbon positive electrode, electrolyte, modified separator, electrolyte, lithium negative electrode, steel sheet, spring sheet, and negative electrode shell (the contents of O2 and H2O are both less than 0.01ppm).
[0071] Example 3:
[0072] A method for preparing FeNC / HSs, comprising the following steps:
[0073] Step 1: Synthesis of SiO2 nanospheres
[0074] TEOS (2.7 mL) was added dropwise to a mixture of ethanol (180 mL), concentrated ammonia solution (30 mL), and distilled water (9 mL) under magnetic stirring at room temperature. After an additional 5 hours of stirring, SiO2 nanospheres were collected by centrifugation (8000 rpm, 3 min) and washed three times with distilled water and ethanol. The collected nanospheres were then dried overnight at 40 °C in a vacuum drying oven, and the dried white powder was ground for further use.
[0075] Step 2: Fe 3+ Preparation of PDA@SiO2 nanospheres
[0076] 2 g SiO2 was dispersed in 200 ml deionized water and sonicated for 2 h. Then, 0.625 g dopamine hydrochloride and 0.2 mmol Fe(NO3)3·9H2O were added to the solution to form a metal complex. After 15 minutes, 0.24 g Tris was added to the solution to initiate the polymerization of dopamine. After stirring continuously at room temperature for 24 h, the black precipitate was collected by centrifugation and washed three times with water and ethanol to obtain Fe. 3+ -PDA@SiO2 nanospheres.
[0077] Step 3: Synthesis of Fe-NC@SiO2 nanospheres
[0078] The synthesized Fe 3+ - The PDA@SiO2 precursor was placed in a tube furnace and heated to 950°C under N2 flow at a heating rate of 5°C / min. -1 Pyrolysis for 3 hours.
[0079] Step 4: Post-processing
[0080] The obtained Fe-NC@SiO2 nanosphere sample was immersed in 5 mol / L NaOH for 48 hours to remove the SiO2 template, followed by washing with deionized water multiple times until the pH reached neutral, and then drying in a vacuum oven at 60°C overnight. Finally, NFP-FeNC / HSs were obtained.
[0081] Step 5: Diaphragm Preparation
[0082] The PFB-FeNC / HSs modified membrane was prepared by a simple vacuum filtration method. 70 wt% PFB-FeNC / HSs, 20 wt% PVDF, and 10 wt% Super-P were mixed in N-methyl-2-pyrrolidone (NMP) solvent and ultrasonically dispersed for 2 h. Then, standard vacuum filtration was performed using a commercially available polypropylene (PP, Celgard 2500) membrane as the filter. Finally, the modified membrane was dried under vacuum at 60 °C for 12 h. The coating quality was controlled to be within 0.47 mg / cm³. -2 The coating thickness is controlled between 25 and 40 μm.
[0083] Step 6: Preparation of sulfur-carbon cathode
[0084] Sulfur-carbon composite material was prepared as the cathode active material via melt diffusion (155℃, 12h), with a sulfur to MWCNTs mass ratio of 3:1 (named S@MWCNTs). The obtained sulfur-carbon composite material, Super-P, and PVDF were mixed at a mass ratio of 8:1:1 using NMP as a solvent and homogenized by hand milling. The slurry was then coated onto carbon-coated aluminum foil using a doctor blade with a blade height of 150 μm. The electrode was then dried in a vacuum oven at 50℃ for 12h. The resulting lithium-sulfur battery cathode electrode had a sulfur loading of approximately 1.0-1.5 mg / cm³. -2 .
[0085] Step 7: Battery fabrication
[0086] In a glove box, a button cell is assembled in the following order: positive electrode shell, sulfur-carbon positive electrode, electrolyte, modified separator, electrolyte, lithium negative electrode, steel sheet, spring sheet, and negative electrode shell (the contents of O2 and H2O are both less than 0.01ppm).
[0087] Comparative Example 1:
[0088] A method for preparing a membrane-free modified lithium-sulfur battery, comprising the following steps:
[0089] Step 1: Preparation of sulfur-carbon cathode
[0090] Sulfur-carbon composite material was prepared as the cathode active material via melt diffusion (155℃, 12h), with a sulfur to MWCNTs mass ratio of 3:1 (named S@MWCNTs). The obtained sulfur-carbon composite material, Super-P, and PVDF were mixed at a mass ratio of 8:1:1 using NMP as a solvent and homogenized by hand milling. The slurry was then coated onto carbon-coated aluminum foil using a doctor blade with a blade height of 150 μm. The electrode was then dried in a vacuum oven at 50℃ for 12h. The resulting lithium-sulfur battery cathode electrode had a sulfur loading of approximately 1.0-1.5 mg / cm³. -2 .
[0091] Step 2: Battery fabrication
[0092] In a glove box, a button cell is assembled in the following order: positive electrode shell, sulfur-carbon positive electrode, electrolyte, PP separator, electrolyte, lithium negative electrode, steel sheet, spring sheet, and negative electrode shell (the contents of O2 and H2O are both less than 0.01ppm).
[0093] Figure 1 The images shown are SEM images of Fe-NC / HSs prepared in Example 1 of this invention, where (a) is a low-magnification image and (b) is a high-magnification image. Figure 1 (c) is a SEM image of Comparative Example 1 of the present invention. Figure 1It can be seen that the particle size of the NFP-FeNC / HSs synthesized with the aid of ionic liquid is significantly reduced.
[0094] Figure 2 The figures show the cyclic voltammetry (CV) curves of the lithium-sulfur batteries corresponding to Examples 1, 1, and 2 of this invention. The lithium-sulfur batteries modified with NFP-FeNC / HSs separators exhibited higher reduction voltages (2.281 V and 1.944 V) and lower oxidation voltages (2.476 V), as well as higher redox peak currents. This indicates that the small-particle-size NFP-FeNC / HSs synthesized via ionic liquids promoted the catalytic conversion of polysulfides, significantly improving redox kinetics.
[0095] Figure 3 The figures show the impedance diagrams of lithium-sulfur batteries corresponding to Embodiments 1, 2, 3, and Comparative Example 1 of the present invention. As can be seen from the figures, the impedance of Embodiment 1 is lower than that of Embodiments 2, 3, and Comparative Example 1.
[0096] Figure 4 The graphs show the 0.2C cycle performance of lithium-sulfur batteries corresponding to Examples 1, 2, 3, and Comparative Example 1 of this invention. The lithium-sulfur battery modified with NFP-FeNC / HSs separator has an initial discharge specific capacity of 1495.9 mAh / g at 0.2C rate, and still has a specific capacity of 867.9 mAh / g after 150 cycles, which is stronger than the cycle performance of the other comparative examples.
[0097] This invention utilizes an ionic liquid (1-hexyl-3-methylimidazolium hexafluorophosphate) to synthesize Fe-NC / HSs. Ionic liquid doping introduces heteroatoms such as N, O, and P, effectively increasing the defect density of carbon nanospheres and significantly expanding their surface area, thus allowing for higher metal atom doping. Subsequent high-temperature pyrolysis forms single metal atoms and a nitrogen-doped carbon framework. The monodisperse metal atoms exhibit very high catalytic activity towards polysulfides, efficiently utilizing polysulfides dissolved from the cathode, greatly improving the utilization rate of active materials, and significantly suppressing the shuttle effect, resulting in a high-performance lithium-sulfur battery. Furthermore, the Fe-NC / HSs prepared in this invention, when used for lithium-sulfur battery separator modification, demonstrates a significant catalytic conversion effect on polysulfides generated in the lithium-sulfur battery. At 0.2C, the initial charge-discharge specific capacity of the lithium-sulfur battery reaches 1400 mAh / g, exhibiting high discharge capacity and excellent cycle stability and rate performance; the first-cycle discharge specific capacity and capacity retention are both higher than those of the comparative example. Regarding battery impedance data, the lithium-sulfur batteries prepared using the Fe-NC / HSs modified separator of this invention all have lower impedances than the comparative examples (…). Figure 3 Furthermore, in the redox kinetics test, the lithium-sulfur battery corresponding to the example showed the smallest peak potential difference in the CV plot, indicating a significant improvement in redox kinetics.
[0098] This invention utilizes 1-hexyl-3-methylimidazolium hexafluorophosphate ionic liquid-assisted synthesis of Fe-NC precursor, followed by direct pyrolysis of Fe 3+ -PDA@SiO2 converts the coated polydopamine into carbon, yielding Fe-NC@SiO2 nanospheres. Finally, etching the SiO2 template with a high-concentration NaOH solution followed by a second high-temperature calcination produces unique Fe-NC / HSs, thus preparing NFP-FeNC / HSs. This method is simple and controllable. When applied to modify lithium-sulfur battery separators, this material effectively alleviates the shuttle effect of polysulfides in lithium-sulfur batteries, catalyzes the conversion of polysulfides, and promotes the redox reaction kinetics during charge and discharge, thereby improving the battery's discharge capacity and cycle stability.
[0099] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions or improvements within the spirit of the present invention are covered within the scope of the claims of the present invention.
Claims
1. A method for preparing Fe-NC single-atom catalyst materials using ionic liquid-assisted synthesis, characterized in that, It includes the following steps: Step 1: Preparation of SiO2 nanosphere template: Tetraethoxysilane was added dropwise to a mixed solution of ethanol, concentrated ammonia solution and distilled water under stirring at room temperature. After stirring, SiO2 nanospheres were collected by centrifugation and washed with distilled water and ethanol. The collected nanospheres were then dried and the dried white powder was ground for later use. Step 2: Fe 3+ Preparation of PDA@SiO2 nanospheres: Dopamine monomer and Fe 3+ The solution chelates with the aid of 1-hexyl-3-methylimidazolium hexafluorophosphate ionic liquid and self-polymerizes on SiO2 nanospheres in a weakly alkaline solution to form a core-shell Fe. 3+ -PDA@SiO2 nanospheres; Step 3: Carbonization: The Fe obtained in Step 2... 3+ - PDA@SiO2 nanospheres were calcined and cooled to obtain carbon-encapsulated silica nanospheres with Fe metal single atoms dispersed. Step 4: Post-processing: The SiO2 template is etched with a high-concentration NaOH solution and then subjected to a second high-temperature calcination to obtain the Fe-NC single-atom catalyst material synthesized with ionic liquid assistance.
2. The preparation method according to claim 1, characterized in that: In step one, the amount of tetraethoxysilane is 2.7 mL; the amount of ethanol is 180 mL, the volume is 30 mL, and the amount of distilled water is 9 mL; the stirring time in step one is 24 h; the centrifugation speed is 6000-8000 r / min, and the time is 2-5 min; the drying temperature is 50-70℃, and the time is 12-24 h; and the concentration of the concentrated ammonia solution is 25-28%.
3. The preparation method according to claim 1, characterized in that: Fe in step two 3+ The solution is Fe(NO3)3·9H2O, and the weakly alkaline solution is tris(hydroxymethyl)aminomethane.
4. The preparation method according to claim 1, characterized in that: In step three, the calcination atmosphere is nitrogen, the calcination temperature is 950℃, the calcination time is 3h, and the heating rate is 5℃ / min.
5. The preparation method according to claim 1, characterized in that: In step four, the NaOH concentration is 5 mol / L, the soaking time is 24 h, and the temperature is 60 °C.
6. A Fe-NC single-atom catalyst material prepared by the preparation method according to any one of claims 1-5.
7. A modified diaphragm, characterized in that, The modified membrane comprises: a membrane, and a modification layer formed on the surface of the membrane comprising the Fe-NC single-atom catalyst material as described in claim 6.
8. The modified diaphragm according to claim 7, characterized in that: The thickness of the modified layer is 25–40 μm; the modified layer also includes a binder and a conductive agent; the binder is polyvinylidene fluoride; the conductive agent is conductive carbon black; the mass ratio of the Fe-NC single-atom catalyst material, binder, and conductive agent is 8:1:
1.
9. A lithium-sulfur battery, characterized in that, It includes: Sulfur-carbon cathode; modified separator as described in claim 7; Lithium anode; and electrolyte.
10. The lithium-sulfur battery according to claim 8, characterized in that, The lithium-sulfur battery is assembled in the following order to form a button cell: positive electrode shell, sulfur-carbon positive electrode, electrolyte, modified separator, electrolyte, lithium negative electrode, steel sheet, spring sheet and negative electrode shell.