Ultrathin porous FeOOH nanosheet, rapid preparation method thereof and application of ultrathin porous FeOOH nanosheet in lithium-sulfur battery diaphragm

Abstract

The invention provides an ultrathin porous FeOOH nanosheet as well as a rapid preparation method and application thereof in a lithium-sulfur battery diaphragm. According to the ultrathin porous FeOOH nanosheet, metal iron is used as a working electrode, a counter electrode is arranged, foam iron is subjected to electrochemical stripping in an electrolyte in a constant-voltage mode, and the ultrathin porous FeOOH nanosheet can be prepared by reacting for 1-5 minutes in a voltage range of 10-20V. Compared with the prior art, the method for rapidly preparing the porous ultrathin FeOOH nanosheet has the advantages that the porous ultrathin FeOOH nanosheet is of a porous and ultrathin structure, the thickness is 3-6 nm, a large number of holes are formed in the surface, and the average pore size is 5-20 nm. The surface of the diaphragm is modified with the graphene, so that the chemical adsorption effect on lithium polysulfide is enhanced, and the coulombic efficiency and the cycling stability of the battery are improved; and moreover, a convenient channel is provided for diffusion of lithium ions, the diffusion path of the lithium ions is shortened, the charge-discharge reaction kinetics of the battery is accelerated, and the charge-discharge efficiency of the battery is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of battery materials, and particularly relates to an ultrathin porous FeOOH nanosheet and a rapid preparation method thereof and application of the ultrathin porous FeOOH nanosheet in a lithium-sulfur battery diaphragm. BACKGROUND

[0002] With the development of new energy, lithium-sulfur batteries are developing faster and faster due to their high energy density. However, the commercialization process of lithium-sulfur batteries is currently encountering many challenges. In the charge-discharge cycle, the shuttle effect caused by soluble lithium polysulfide intermediates (Li2Sn, 4≤n≤8) leads to irreversible loss of active materials and accelerates corrosion of the lithium negative electrode. In addition, the insulating properties of sulfur and its discharge products greatly slow down the kinetics of the electrode reaction, and the slow kinetics of the polysulfide conversion reaction also seriously limits the rate performance of the battery. These problems have become key bottlenecks restricting the industrialization and application of lithium-sulfur batteries.

[0003] To solve these problems, diaphragm functionalization modification has become one of the most promising directions. Traditional polyolefin diaphragms (PE / PP) cannot solve the above problems. Therefore, more and more technical researches on two-dimensional material modified diaphragm systems, which realize the adsorption-charge transfer-catalytic conversion of lithium polysulfide, are the key to improving the comprehensive performance of lithium-sulfur batteries.

[0004] Some transition metal compounds with a two-dimensional structure have certain advantages in this field. Among them, iron-based materials are widely concerned due to their price advantage, and FeOOH materials have advantages in adsorbing polysulfides, accelerating electrochemical reactions, and buffering volume expansion. At present, the preparation process of common FeOOH and corresponding derivative materials is mainly based on hydrothermal and solvothermal methods. For example, the patent with the publication number CN110061220A disclosed on July 26, 2019 discloses a FeOOH / graphene active material and a preparation method thereof, and a lithium-sulfur battery positive electrode material and a preparation method thereof. Although the hydrothermal reaction principle is simple, there are still disadvantages such as high reaction temperature (100-200℃) and long process time (3-10h).

[0005] Therefore, it is still a challenge to provide a fast, simple and low-consumption preparation technology of FeOOH nanosheet. SUMMARY

[0006] The purpose of the present application is to provide an ultrathin porous FeOOH nanosheet and a rapid preparation method thereof. The FeOOH nanosheet material can be obtained in a very short time by using an electrochemical system to anodically oxidize and strip the foam iron. The preparation method is simple and has low energy consumption.

[0007] Another objective of this invention is to provide an application of ultrathin porous FeOOH nanosheets in lithium-sulfur battery separators. By modifying the surface of lithium-sulfur battery separators with ultrathin porous FeOOH nanosheets, a heterogeneous interface with synergistic effects such as adsorption, charge transfer, and catalytic conversion is constructed, effectively solving key problems such as capacity decay and limited rate performance caused by polysulfide shuttle effect in lithium-sulfur batteries.

[0008] The specific technical solution of this invention is as follows:

[0009] A rapid preparation method for ultrathin porous FeOOH nanosheets, specifically as follows:

[0010] Using metallic iron as the working electrode and setting a counter electrode, the foamed iron is electrochemically stripped in an electrolyte using a constant voltage mode to obtain the desired product.

[0011] The electrolyte is a mixed solution of KOH, NaH2PO4 and KCl;

[0012] The KOH concentration in the mixed solution is 0.1–0.2 g / mL.

[0013] The concentration of NaH2PO4 in the mixed solution is 0.2–0.4 g / mL.

[0014] The KCl concentration in the mixed solution is 0.1–0.3 g / mL.

[0015] The metallic iron is selected from one of foamed iron, iron sheet, and iron rod electrodes;

[0016] The counter electrode is one of a carbon rod electrode, a metallic iron electrode, or a metallic nickel electrode.

[0017] The electrochemical stripping of the foamed iron is carried out using a constant voltage mode, with a constant voltage range of 10–20V; the constant voltage reaction time is 1–5 min, preferably 1–3 min.

[0018] Electrochemical stripping produces a precipitate that is dispersed in solution. The precipitate is then separated by centrifugation, washed, and dried to obtain the FeOOH product.

[0019] In this invention, metallic iron is used as the working electrode, and a counter electrode is set up to construct a two-electrode system in an electrolyte for anodic oxidation. This invention employs electrochemical anodic oxidation technology, using elemental iron as the raw material, to achieve rapid preparation of FeOOH. First, metallic iron (elemental iron) is placed in a specific electrolyte solution. Utilizing the principle of electrochemical anodic oxidation, by applying a suitable voltage, the metal atoms on the iron surface undergo an oxidation reaction, and the dihydrogen phosphate ions are then stripped away, resulting in FeOOH rich in active sites. The generated FeOOH possesses unique structural characteristics, with a regular crystal structure and abundant catalytic and adsorption sites. Simultaneously, strong Fe-O-Fe chemical bonds are formed at the FeOOH crystal interface. This chemical bonding greatly facilitates the rapid charge transport within the material, significantly improving its electrical properties. From the perspective of active sites, this preparation method achieves a synergistic effect of dual active sites. The special structure produced by anodic oxidation etching provides FeOOH with a large number of catalytic conversion active centers. These active centers can effectively synergistically lower the Li2S decomposition barrier and accelerate the electrochemical reaction rate. The structural characteristics of FeOOH make it an excellent adsorption site for lithium polysulfides, which can effectively suppress the shuttle effect in lithium-sulfur batteries.

[0020] This invention provides an ultrathin porous FeOOH nanosheet, prepared using the aforementioned rapid preparation method. The ultrathin porous FeOOH nanosheet is a layered structure of two-dimensional FeOOH nanosheets, with a thickness of 3–6 nm and numerous pores on its surface, with an average pore size of 5–20 nm.

[0021] This paper provides an application of ultrathin porous FeOOH nanosheets in lithium-sulfur battery separators. The ultrathin porous FeOOH nanosheets are used to modify the surface of the lithium-sulfur battery separator. The specific application method is as follows:

[0022] Ultrathin porous FeOOH nanosheets, carbon nanotubes, and PVDF binder were dispersed in NMP (N-methylpyrrolidone) solvent. After the resulting slurry was uniformly stirred, it was coated onto the surface of the separator using a doctor blade coating technique. The mixture was then vacuum dried at 60°C until the NMP solvent evaporated, resulting in a modified separator for lithium-sulfur batteries.

[0023] The mass ratio of the ultrathin porous FeOOH nanosheets, carbon nanotubes, and PVDF binder is 7:2:1.

[0024] The thickness of the mixed slurry on the diaphragm surface after drying is 7 μm.

[0025] FeOOH nanosheets significantly enhance battery performance through the following synergistic mechanisms: the high polarity of the FeOOH component promotes the effective adsorption of lithium polysulfides; the abundant surface oxygen vacancies in the two-dimensional structure provide strong chemisorption sites; the surface electron transfer kinetics are modulated by oxygen coordination loss; and the residual ligand oxygen can act as a co-catalyst to promote the sulfur reduction reaction. Simultaneously, oxygen vacancies enhance conductivity and accelerate electron refilling, thereby promoting the smooth conversion of sulfur and improving the battery's reversible capacity. This innovative design provides a new material solution for developing high-performance lithium-sulfur batteries.

[0026] The two-dimensional FeOOH nanosheets provided by this invention, as a separator modification layer for lithium-sulfur batteries, offer key advantages in suppressing the polysulfide shuttle effect and catalytically transforming reaction kinetics. On one hand, the two-dimensional structure possesses a large specific surface area, providing abundant active sites, increasing the contact area with lithium polysulfides, enhancing the chemisorption of lithium polysulfides, and effectively suppressing the shuttle effect of lithium polysulfides in the electrolyte, thereby reducing the loss of active materials and improving the coulombic efficiency and cycle stability of the battery. The layered structure (thickness 3–6 nm) of the two-dimensional FeOOH nanosheets facilitates the rapid transport of lithium ions and electrons. Numerous surface pores (average pore size approximately 5–20 nm) not only promote electrolyte wetting but also provide convenient channels for lithium ion diffusion, shortening the lithium ion diffusion path and accelerating the charge-discharge reaction kinetics of the battery. On the other hand, FeOOH promotes the effective adsorption and catalytic reaction of lithium polysulfides. Its surface oxygen vacancies provide strong chemisorption and catalytic sites, effectively reducing the activation energy of the conversion reaction of soluble lithium polysulfides to the final product Li2S, promoting the sulfur reduction reaction process, reducing the battery internal resistance, and improving the battery's charge and discharge efficiency.

[0027] Compared with existing technologies, this invention provides a method for rapidly preparing porous ultrathin FeOOH nanosheets with a porous and ultrathin structure. Modifying these nanosheets on the surface of a separator not only enhances the chemical adsorption of lithium polysulfides, improving the coulombic efficiency and cycle stability of the battery, but also provides a convenient channel for lithium ion diffusion, shortening the lithium ion diffusion path, accelerating the charge-discharge reaction kinetics of the battery, and improving the charge-discharge efficiency of the battery. Attached Figure Description

[0028] Figure 1 The XRD pattern of the FeOOH nanosheets prepared in Example 1;

[0029] Figure 2 This is a TEM image of the FeOOH nanosheets prepared in Example 1;

[0030] Figure 3 Cyclic testing was conducted on Comparative Example 1 (a battery assembled with a common commercial PP separator) and the battery assembled with FeOOH nanosheets prepared in Example 1 as a separator modification layer.

[0031] Figure 4 The XRD pattern of the FeOOH nanosheets prepared in Example 2;

[0032] Figure 5 This is a TEM image of the FeOOH nanosheets prepared in Example 2;

[0033] Figure 6 Cyclic testing was conducted on Comparative Example 1 (a battery assembled with a common commercial PP separator) and the battery assembled with FeOOH nanosheets prepared in Example 2 as a separator modification layer.

[0034] Figure 7 The XRD pattern of the FeOOH nanosheets prepared in Example 3;

[0035] Figure 8 This is a TEM image of the FeOOH nanosheets prepared in Example 3;

[0036] Figure 9 Cyclic testing was conducted on Comparative Example 1 (a battery assembled with a common commercial PP separator) and the battery assembled with FeOOH nanosheets prepared in Example 3 as a separator modification layer.

[0037] Figure 10 The image shows a TEM image of FeOOH obtained in Comparative Example 2.

[0038] Figure 11 This is a TEM image of FeOOH obtained in Comparative Example 3. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0041] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0042] Example 1

[0043] A rapid preparation method for ultrathin porous FeOOH nanosheets includes the following steps:

[0044] 1) Weigh 35g of KOH and dissolve it in 200mL of deionized water to form a solution;

[0045] 2) Add 50g of NaH2PO4 solid to the solution obtained in step 1), stir to dissolve, and form a mixed solution;

[0046] 3) Add 30g of KCl solid to the mixed solution obtained in step 2), stir to dissolve, and obtain a mixed solution;

[0047] 4) Using the mixed solution obtained in step 3) as the electrolyte, foamed iron as the working electrode, and carbon rod as the counter electrode, a two-electrode system is constructed.

[0048] 5) Perform an anodic oxidation reaction on the two-electrode system in step 4). Use a constant voltage mode of 15V to perform electrochemical oxidation reaction on the foamed iron and continue for 3 minutes to obtain a suspension.

[0049] 6) After step 5) above is completed, the precipitate is centrifuged, washed repeatedly with deionized water until the pH of the supernatant is neutral, and then dried at 40°C to finally obtain the FeOOH product.

[0050] The final product sample was characterized by X-ray powder diffraction (XRD). Figure 1 The sample exhibits distinct FeOOH characteristic peaks, with the crystal planes corresponding to 14.1°, 27.1°, 36.2°, 46.9°, and 60.7° being (020), (021), (130), (002), and (171) planes, respectively. The morphology of the sample was characterized using scanning electron microscopy (TEM). Figure 2 It can be seen that the prepared FeOOH has the morphology of nanosheets with a size of about 50-150 nm and a thickness of 3-6 nm. At the same time, the surface has a certain porosity, with an average pore size of about 5-20 nm.

[0051] When the ultrathin porous FeOOH nanosheets prepared in Example 1 above are applied to the modification of lithium-sulfur battery separators, the specific steps are as follows:

[0052] A. Accurately weigh the ultrathin porous FeOOH nanosheets, carbon nanotubes, and polyvinylidene fluoride binder (PVDF) prepared in Example 1 according to a mass ratio of 7:2:1. Add them sequentially to N-methylpyrrolidone (NMP) solvent at a ratio of 1g solid to 20mL solvent. Stir magnetically to ensure a stable and dispersed slurry system. Using a doctor blade coating technique, uniformly coat the prepared slurry onto the surface of a commercial PP separator, Celgard 2500. After vacuum drying at 60°C, a modified layer with a thickness of 7μm is finally formed, suitable for high-performance modified separators in lithium-sulfur batteries.

[0053] B. CNTs and sulfur powder are mixed at a mass ratio of 3:7, and then dispersed with acetylene black and PVDF in an 8:1:1 ratio in NMP solvent, using a ratio of 1g solid to 20mL solvent. The mixture is stirred and sonicated to form a positive electrode slurry, which is then coated with aluminum foil and dried to form the electrode sheet. The negative electrode uses a lithium metal sheet. The electrolyte is prepared by dissolving 1mol / L LiTFSI and 0.2mol / L LiNO3 in a 1:1 volume ratio of DOL / DME mixed solvent. In an argon-filled glove box, the positive and negative electrode sheets are stacked with a modified separator, and the electrolyte is injected to complete the battery encapsulation.

[0054] Comparative Example 1

[0055] This comparative example compares the effect of using a conventional PP separator in a lithium-sulfur battery with the modified battery of Example 1 on electrochemical and cycle performance. The preparation steps of the comparative battery are as follows:

[0056] CNTs and sulfur powder were mixed at a mass ratio of 3:7, and then dispersed with acetylene black and PVDF in NMP solvent at a ratio of 8:1:1. The mixture was stirred and sonicated to form a positive electrode slurry, which was then coated with aluminum foil and vacuum dried at 40°C to obtain the electrode sheet. The negative electrode used was a lithium metal sheet, with an electrolyte prepared by dissolving 1 mol / L LiTFSI and 0.2 mol / L LiNO3 in a 1:1 volume ratio of DOL / DME. The positive and negative electrodes were stacked with a standard separator in an argon-filled glove box, and electrolyte was injected to complete the battery encapsulation.

[0057] The battery assembled with the FeOOH modified separator prepared in Example 1 and the battery of Comparative Example 1 were subjected to a charge-discharge test of 100 cycles at a rate of 0.5C (temperature 25°C, voltage range 1.7–2.8V).

[0058] from Figure 3 It can be seen that at a discharge rate of 0.5C, the initial discharge specific capacity of the prepared membrane-modified battery after stabilization is 886 mAh / g, while that of the comparative example is 775 mAh / g. This is because the FeOOH modified material on the separator can catalyze and accelerate the reaction rate of lithium polysulfide conversion, enhance reaction kinetics, and thus improve the utilization rate of active materials. After 100 cycles, the specific capacity of the modified separator battery is 612 mAh / g, while that of the comparative example 1 battery is 433 mAh / g. The former has a capacity retention rate of 69.1%, which is much higher than the latter's 55.9%. This is because the membrane modification layer chemically interacts with soluble polysulfides through chemical bonding. The soluble polysulfides are adsorbed on the FeOOH surface, which greatly suppresses the "shuttle effect" in the bulk phase of the lithium-sulfur battery, thereby improving the cycle stability of the capacity.

[0059] Example 2

[0060] A rapid preparation method for ultrathin porous FeOOH nanosheets includes the following steps:

[0061] 1) Weigh 40g of KOH and dissolve it in 200mL of deionized water to form a solution;

[0062] 2) Add 50g of NaH2PO4 solid to the solution obtained in step 1), stir to dissolve, and form a mixed solution;

[0063] 3) Add 25g of KCl solid to the mixed solution obtained in step 2), stir to dissolve, and obtain a mixed solution;

[0064] 4) Using the mixed solution obtained in step 3) as the electrolyte, foamed iron as the working electrode, and carbon rod as the counter electrode, a two-electrode system is constructed.

[0065] 5) Perform an anodic oxidation reaction on the two-electrode system in step 4). Use a constant voltage mode of 20V to perform electrochemical oxidation reaction on the foamed iron and continue for 1.5min to obtain a suspension.

[0066] 6) After step 5) above is completed, the precipitate is centrifuged, washed repeatedly with deionized water until the pH of the supernatant is neutral, and then dried at 40°C to finally obtain the FeOOH product.

[0067] The final product sample was characterized by X-ray powder diffraction (XRD). Figure 4 Five characteristic peaks of FeOOH can be clearly seen in the image, corresponding to the (020), (021), (130), (002), and (171) crystal planes, indicating the successful preparation of FeOOH. The morphology of the prepared FeOOH was characterized by scanning electron microscopy (TEM). Figure 5 It can be seen that FeOOH has a distinct nanosheet structure and a porous surface.

[0068] The application of the FeOOH nanosheets prepared in Example 2 above in the modification of lithium-sulfur battery separators is as follows:

[0069] A. Accurately weigh the FeOOH nanosheets, carbon nanotubes, and polyvinylidene fluoride binder (PVDF) prepared in Example 2 according to a mass ratio of 7:2:1, and sequentially add them to N-methylpyrrolidone (NMP) solvent at a ratio of 1g solid to 20mL solvent. Magnetic stirring ensures the formation of a stable and dispersed slurry system. Using a doctor blade coating technique, uniformly coat the prepared slurry onto the surface of a commercial PP separator. After vacuum drying, a modified layer with a thickness of 7μm is finally formed, suitable for high-performance modified separators in lithium-sulfur batteries.

[0070] B. CNTs and sulfur powder are mixed at a mass ratio of 3:7, and then dispersed with acetylene black and PVDF in an 8:1:1 ratio in NMP solvent, using a ratio of 1g solid to 20mL solvent. The mixture is stirred and sonicated to form a positive electrode slurry, which is then coated with aluminum foil and dried to form the electrode sheet. The negative electrode uses a lithium metal sheet. The electrolyte is prepared by dissolving 1mol / L LiTFSI and 0.2mol / L LiNO3 in a 1:1 volume ratio of DOL / DME mixed solvent. In an argon-filled glove box, the positive and negative electrode sheets are stacked with a modified separator, and the electrolyte is injected to complete the battery encapsulation.

[0071] The battery assembled with the FeOOH modified separator prepared in Example 2 and the battery of Comparative Example 1 were subjected to a charge-discharge test of 100 cycles at a rate of 0.5C (temperature 25°C, voltage range 1.7~2.8V).

[0072] from Figure 6 It can be seen that the initial discharge specific capacity of the membrane-modified battery in Example 2 after stabilization is 844 mAh / g, and the capacity after 100 cycles is 721 mAh / g, with a corresponding retention rate of 85.4%, which is significantly better than the ordinary PP membrane battery in Comparative Example 1.

[0073] Example 3

[0074] A rapid preparation method for ultrathin porous FeOOH nanosheets includes the following steps:

[0075] 1) Weigh 30g of KOH and dissolve it in 200mL of deionized water to form a solution;

[0076] 2) Add 60g of NaH2PO4 solid to the solution obtained in step 1), stir to dissolve, and form a mixed solution;

[0077] 3) Add 30g of KCl solid to the mixed solution obtained in step 2) and stir to dissolve;

[0078] 4) Using the mixed solution obtained in step 3) as the electrolyte, foamed iron as the working electrode, and carbon rod as the counter electrode, a two-electrode system is constructed.

[0079] 5) Perform an anodic oxidation reaction on the two-electrode system in step 4). Use a constant voltage mode of 17V to perform electrochemical oxidation reaction on the foamed iron and continue for 2 minutes to obtain a suspension.

[0080] 6) After step 5) above is completed, the precipitate is centrifuged, washed repeatedly with deionized water until the pH of the supernatant is neutral, and then dried at 40°C to finally obtain the FeOOH product.

[0081] The final product sample was characterized by X-ray powder diffraction (XRD). Figure 7As can be seen from the spectrum, more pronounced FeOOH characteristic peaks appear, with 14.1°, 27.1°, 36.2°, 46.9°, and 60.7° corresponding to the (020), (021), (130), (002), and (171) crystal planes, respectively. This was confirmed by projection electron microscopy (TEM). Figure 8 A porous sheet structure with FeOOH morphology was discovered.

[0082] The application of the FeOOH nanosheets prepared in Example 3 above in the modification of lithium-sulfur battery separators is as follows:

[0083] A. Accurately weigh the FeOOH nanosheets, carbon nanotubes, and polyvinylidene fluoride binder (PVDF) prepared in Example 3 according to a mass ratio of 7:2:1, and sequentially add them to N-methylpyrrolidone (NMP) solvent at a ratio of 1g solid to 20mL solvent. Magnetic stirring ensures the formation of a stable and dispersed slurry system. Using a doctor blade coating technique, uniformly coat the prepared slurry onto the surface of a commercial PP separator. After vacuum drying, a modified layer with a thickness of 7μm is finally formed, suitable for high-performance modified separators in lithium-sulfur batteries.

[0084] B. CNTs and sulfur powder are mixed at a mass ratio of 3:7, and then dispersed with acetylene black and PVDF in an 8:1:1 ratio in NMP solvent, using a ratio of 1g solid to 20mL solvent. The mixture is stirred and sonicated to form a positive electrode slurry, which is then coated with aluminum foil and dried to form the electrode sheet. The negative electrode uses a lithium metal sheet. The electrolyte is prepared by dissolving 1mol / L LiTFSI and 0.2mol / L LiNO3 in a 1:1 volume ratio of DOL / DME mixed solvent. In an argon-filled glove box, the positive and negative electrode sheets are stacked with a modified separator, and the electrolyte is injected to complete the battery encapsulation.

[0085] The batteries assembled in Example 3 and the batteries in Comparative Example 1 were subjected to a charge-discharge test at a rate of 0.5C for 100 cycles, at a temperature of 25°C and a voltage range of 1.7 to 2.8V.

[0086] from Figure 9 It can be seen that the initial discharge specific capacity of the membrane-modified battery in Example 3 after stabilization is 863 mAh / g, and the capacity retention rate is 74.3% after 100 cycles. In contrast, the initial capacity of the ordinary PP membrane battery in the comparison sample is only 775 mAh / g, and the capacity retention rate is only 55.9%. This shows that the prepared FeOOH effectively improves the electrochemical performance of lithium-sulfur batteries.

[0087] Comparative Example 2

[0088] This comparative example is used to illustrate the effect of electrolyte alkalinity on the morphology of the final product. The specific preparation steps are as follows:

[0089] 1) Weigh 40g of LiOH and dissolve it in 200mL of deionized water to form a solution;

[0090] 2) Add 50g of NaH2PO4 solid to the solution obtained in step 1), stir to dissolve, and form a mixed solution;

[0091] 3) Add 25g of KCl solid to the mixed solution obtained in step 2) and stir to dissolve;

[0092] 4) Using the mixed solution obtained in step 3) as the electrolyte, foamed iron as the working electrode, and carbon rod as the counter electrode, a two-electrode system is constructed.

[0093] 5) Perform an anodic oxidation reaction on the two-electrode system in step 4). Use a constant voltage mode of 20V to perform electrochemical oxidation reaction on the foamed iron and continue for 3 minutes to obtain a suspension.

[0094] 6) After step 5) above is completed, the precipitate is centrifuged, washed repeatedly with deionized water until the pH of the supernatant is neutral, and then dried at 40°C to finally obtain the FeOOH product.

[0095] By projection electron microscopy (TEM) Figure 10 It was found that the morphology of FeOOH was still a lamellar structure, but the number of surface pores was significantly reduced.

[0096] Comparative Example 3

[0097] This comparative example is used to illustrate the effect of electrolyte alkalinity on the morphology of the final product. The specific preparation steps are as follows:

[0098] 1) Take 100 mL of commercially available ammonia water (mass fraction of about 25%) and dissolve it in 100 mL of deionized water to form a solution;

[0099] 2) Add 50g of NaH2PO4 solid to the solution obtained in step 1), stir to dissolve, and form a mixed solution;

[0100] 3) Add 25g of KCl solid to the mixed solution obtained in step 2) and stir to dissolve;

[0101] 4) Using the mixed solution obtained in step 3) as the electrolyte, foamed iron as the working electrode, and carbon rod as the counter electrode, a two-electrode system is constructed.

[0102] 5) Perform an anodic oxidation reaction on the two-electrode system in step 4). Use a constant voltage mode of 20V to perform electrochemical oxidation reaction on the foamed iron and continue for 3 minutes to obtain a suspension.

[0103] 6) After step 5) above is completed, the precipitate is centrifuged, washed repeatedly with deionized water until the pH of the supernatant is neutral, and then dried at 40°C to finally obtain the FeOOH product.

[0104] By projection electron microscopy (TEM) Figure 11 FeOOH was found to have a lamellar structure, but the surface was smooth and no pores were found.

[0105] The TEM comparisons of Comparative Examples 2, 3 and the Examples show that the alkalinity of the electrolyte has a certain influence on the morphology of the FeOOH nanosheet samples. The stronger the alkalinity, the more obvious the porous structure of the product.

[0106] This invention is based on an electrochemical anodic oxidation process, constructing a high-pressure oxidation reaction system. By controlling the electrode potential, electrons undergo valence state transitions, achieving rapid oxidation from a zero-valence state to a +3 valence state. In the electrolyte system, the alkaline component continuously releases hydroxide ions through hydrolysis equilibrium, which coordinate with the ferric ions generated during oxidation on the anode surface, resulting in the in-situ growth of FeOOH nanocrystal layers on the surface of the metallic iron electrode. During the layered structure construction stage, dihydrogen phosphate ions with a large spatial configuration in the electrolyte embed into the FeOOH layers through an ion exchange mechanism. Utilizing their ionic radius advantage, they generate a lattice expansion effect, weakening the interfacial bonding between FeOOH and the metallic iron substrate. This process is similar to an exfoliation reaction, ultimately causing the FeOOH nanosheets to efficiently detach from the electrode surface, forming a two-dimensional active material with controllable size and morphology.

[0107] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A rapid preparation method for ultrathin porous FeOOH nanosheets, characterized in that, The preparation method is specifically as follows: Using metallic iron as the working electrode and setting a counter electrode, the foamed iron is electrochemically stripped in an electrolyte using a constant voltage mode to obtain the desired product.

2. The rapid preparation method according to claim 1, characterized in that, The electrolyte is a mixed solution of KOH, NaH2PO4 and KCl.

3. The rapid preparation method according to claim 2, characterized in that, The KOH concentration in the mixed solution is 0.1–0.2 g / mL.

4. The rapid preparation method according to claim 2, characterized in that, The concentration of NaH2PO4 in the mixed solution is 0.2–0.4 g / mL.

5. The rapid preparation method according to claim 2, characterized in that, The KCl concentration in the mixed solution is 0.1–0.3 g / mL.

6. The rapid preparation method according to claim 2, characterized in that, The metallic iron is selected from one of the following: foamed iron, iron sheet, and iron rod electrode.

7. The rapid preparation method according to claim 2, characterized in that, The electrochemical stripping of the foamed iron was carried out using a constant voltage mode, with a constant voltage range of 10–20V and a constant voltage duration of 1–5 min.

8. An ultrathin porous FeOOH nanosheet, prepared by the rapid preparation method according to any one of claims 1-7; characterized in that, The ultrathin porous FeOOH nanosheets are layered structures of two-dimensional FeOOH nanosheets with a thickness of 3-6 nm and pores on the surface with an average pore size of 5-20 nm.

9. The application of the ultrathin porous FeOOH nanosheets as described in claim 8 in a lithium-sulfur battery separator, characterized in that, Ultrathin porous FeOOH nanosheets were used to modify the surface of lithium-sulfur battery separators.

10. The application according to claim 9, characterized in that, The specific application method is as follows: Ultrathin porous FeOOH nanosheets, carbon nanotubes, and PVDF binder were dispersed in NMP solvent. After the resulting slurry was uniformly stirred, it was coated onto the surface of the separator using a doctor blade coating technique. After vacuum drying and evaporation of the NMP solvent, a modified separator for lithium-sulfur batteries was obtained.

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