A method for preparing tightly connected iron disulfide hollow spheres@graphene microstructures, its products and applications

Abstract

This invention discloses a method for preparing a tightly connected FeS2 hollow sphere@graphene microstructure: S1, ferric nitrate and alcohol are mixed and reacted to obtain a Fe-alcohol complex; S2, dopamine hydrochloride is added to the Fe-alcohol complex, and a polymerization reaction is carried out by stirring; after the polymerization reaction, a cationic surfactant is added; S3, the product obtained in S2 is added to a graphene oxide dispersion, and the reaction is stirred; S4, the product obtained in S3 is calcined for the first time, and sulfur powder is added for the second calcination to obtain a tightly connected FeS2 hollow sphere@graphene microstructure. This invention also provides the tightly connected FeS2 hollow sphere@graphene microstructure obtained by the above preparation method and its application in the anode of potassium-ion batteries. This preparation method achieves a tight connection between FeS2 hollow spheres and graphene, solving the problems of poor electronic conductivity and structural stability of micron-sized FeS2, and achieving excellent rate performance when applied to the anode of potassium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of potassium-ion battery energy storage, and particularly relates to a method for preparing a tightly connected iron disulfide hollow sphere@graphene microstructure, its products, and applications. Background Technology

[0002] Lithium-ion batteries, due to their outstanding energy and power densities, have become one of the most promising energy storage technologies in the field of renewable energy storage and utilization. However, the high price caused by the scarcity and uneven distribution of lithium resources severely limits the future development of lithium-ion batteries, necessitating the development of next-generation low-cost alkali metal-ion batteries to replace lithium-ion batteries for renewable energy storage and utilization. Potassium-based batteries, due to their abundant and inexpensive resources and similar physicochemical properties to lithium-ion batteries, are receiving widespread attention and are expected to become a candidate energy storage technology to replace lithium-ion batteries in the future. However, the current development of potassium-ion batteries is limited by the capacity, rate performance, and stability of the negative electrode. This is mainly because the large atomic size of potassium ions makes it difficult to store ions at the negative electrode, causing significant volume expansion, and potassium ion diffusion and reaction kinetics within the negative electrode material are slow. Pyrite, i.e., FeS2, due to its extremely high capacity and abundant resources, is very promising as a future low-cost negative electrode material for potassium-ion batteries, but its insufficient intrinsic conductivity and large volume expansion lead to slow potassium ion reaction kinetics and significant volume expansion.

[0003] Based on this, improving the conductivity of FeS2 and limiting its volume expansion have become key issues in improving its potassium storage rate performance and stability, and are also important research directions in the design of FeS2 anodes for potassium-ion batteries. Currently, the common approach is to combine nanostructured FeS2 with carbon materials to improve the conductivity and structural stability of FeS2 (e.g., Zhang Z, Duan L, Xu Y, et al. Synthesis of multicore-shell FeS2@C nanocapsules for stable potassiumion batteries[J]. Energy Chemistry: English Edition, 2022(010):000.DOI:10.1016 / j.jechem.2022.04.039. and Wu H, Lu S, Xu S, et al. Blowing Iron Chalcogenides into Two-Dimensional Flaky Hybrids with Superior Cyclability and Rate Capability for Potassium-Ion Batteries[J].[2023-12-25].). However, the widely used FeS2 nanostructures, due to their large specific surface area and surface energy, actually lead to a large amount of self-agglomeration during the preparation process, which is detrimental to the personalized and large-scale preparation of FeS2 materials. Therefore, it is necessary to study the preparation of micron-sized FeS2 materials to achieve the preparation of oriented FeS2 anode materials. However, the preparation of micron-sized FeS2 still faces difficulties. This is mainly because the structural stability of micron-sized FeS2 materials may be more unstable than that of nano-sized FeS2, and its conductivity problem may be more prominent due to its smaller specific surface area. Therefore, it is necessary to develop better FeS2 micron-sized structures to meet this application requirement.

[0004] Therefore, designing more rational micron-structured FeS2 materials to improve potassium storage ratio and stability is currently a technical hotspot and challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a tightly connected FeS2 hollow sphere@graphene microstructure. By introducing a layer of carbon into the FeS2 hollow sphere and graphene network, a tight connection between the FeS2 hollow sphere and graphene is achieved, thereby enabling excellent rate performance and stability when applied to the negative electrode of potassium-ion batteries.

[0006] This invention provides the following technical solution:

[0007] A first aspect of the present invention provides a method for preparing a tightly connected iron disulfide hollow sphere@graphene microstructure, the method comprising the following steps:

[0008] S1. A Fe-alcohol complex is obtained by mixing ferric nitrate and alcohol and reacting them.

[0009] S2. Add dopamine hydrochloride to the Fe-alcohol complex and stir to carry out the polymerization reaction; after the polymerization reaction, add a cationic surfactant.

[0010] S3. Add the product obtained in S2 (polydopamine-coated Fe-alcohol complex) to the graphene oxide dispersion and stir to react;

[0011] S4. The product obtained in S3 is calcined for the first time, and sulfur powder is added for the second calcination to obtain a tightly connected FeS2 hollow sphere@graphene micron structure.

[0012] The technical concept of this invention lies in the fact that by separating the preparation of FeS2 hollow sphere precursors and their composite with graphene into two steps, the agglomeration problem in the in-situ preparation process can be avoided, and more selectivity for directional preparation can be provided. First, the FeS2 hollow sphere precursor (Fe-alcohol composite) is prepared by a solvothermal method. Then, in a buffer solution, the dopamine carbon precursor undergoes a self-polymerization reaction on the surface of the Fe-alcohol composite. Subsequently, by reasonably introducing positively charged particles, a tight connection between the Fe-alcohol composite and graphene is achieved through the electrostatic interaction between the positive charge on the surface of the Fe-alcohol composite and the negative charge on the surface of graphene oxide. This connection is strengthened during subsequent annealing and vulcanization processes, achieving a tight bond between the FeS2 hollow spheres and graphene.

[0013] The tightly connected iron disulfide hollow sphere@graphene micron structure provided by this invention has the following advantages: First, the hollow sphere structure facilitates sufficient electrolyte wetting; second, the close contact between the FeS2 hollow spheres and the graphene layer, achieved through the dopamine interlayer carbon, accelerates the electron transfer process between FeS2 and graphene, while providing reasonable protection for the hollow structure. This structure achieves a rapid ion-electron transport rate and good stability. When applied to the anode of potassium-ion batteries, it achieves excellent rate performance and stability.

[0014] In step S1, the ferric nitrate is one of ferric nitrate nonahydrate or ferric nitrate hexahydrate; the alcohol is selected from isopropanol, glycerol or ethylene glycol.

[0015] In step S1, the reaction temperature is 150–190°C.

[0016] In step S2, the mass ratio of dopamine hydrochloride to the Fe-alcohol complex is 1:1 to 2:1, and the stirring time is 0.5 to 2 hours. When the mass ratio is less than 1:1 and the stirring time is less than 0.5 hours, there is too little dopamine hydrochloride, the polymerization reaction is insufficient, and an appropriate amount of polydopamine cannot be formed on the Fe-alcohol complex. When the mass ratio is greater than 2:1 and the stirring time is greater than 2 hours, there is too little dopamine hydrochloride, and the polymerization reaction is excessive, resulting in the formation of excessive polydopamine on the Fe-alcohol complex, which increases the carbon content and reduces the capacity.

[0017] In step S2, the cationic surfactant is selected from sodium dodecylbenzenesulfonate or polydiallyldimethylammonium chloride. Preferably, the cationic surfactant solution used is one of a 10% sodium dodecylbenzenesulfonate solution and a 10% polydiallyldimethylammonium chloride solution.

[0018] In step S3, the mass ratio of the product obtained in S2 to graphene oxide is 1:2 to 2:1. When the ratio is less than 1:2, the content of graphene oxide is too high, resulting in a decrease in the relative content of the Fe-alcohol complex and a decrease in material capacity; when the ratio is greater than 2:1, the content of graphene oxide is too low, weakening the coating effect on the Fe-alcohol complex.

[0019] In step S4, the temperature of the first calcination is 450–550°C. When the temperature is below 450°C, the carbonization effect of graphene oxide and polydopamine is poor, and the electrical conductivity of the material is not high. When the temperature is above 550°C, the excessive temperature leads to changes in the crystal phase structure, resulting in an impure crystal phase in the obtained material, and the sample is no longer FeS2.

[0020] In step S4, the mass ratio of the sulfur powder to the product after the first calcination is 1:1 to 5:1; the temperature of the second calcination is 350 to 400°C. When the mass ratio is less than 1:1, the sulfur source content is too low and the FeS2 structure cannot be formed; when the mass ratio is greater than 5:1, the sulfur source content is too high, leading to sulfur waste.

[0021] Furthermore, in step S4, argon gas is continuously introduced into the calcining furnace after the heat preservation is stopped as an inert protective gas until the calcined sample cools to room temperature.

[0022] Further preferably, the mass ratio of dopamine hydrochloride to the Fe-alcohol complex is 1:1 to 2:1, the mass ratio of the polydopamine-coated Fe-alcohol complex to graphene oxide is 1:2 to 1.5:2, the first calcination temperature is 450 to 550°C, the second calcination temperature is 400°C, and the mass ratio of sulfur powder to the material is 1:1 to 5:1. The FeS2 hollow sphere@graphene microstructure prepared under the above conditions exhibits high capacity and rate capability.

[0023] Further preferably, the mass ratio of dopamine hydrochloride to the Fe-alcohol complex is 1:1, the mass ratio of the polydopamine-coated Fe-alcohol complex to graphene oxide is 1.5:2, the first calcination temperature is 500℃, the second calcination temperature is 400℃, and the mass ratio of sulfur powder to materials is 5:1. The FeS2 hollow sphere@graphene microstructures prepared under the above conditions exhibit higher capacity and rate capability.

[0024] A second aspect of the present invention provides a tightly connected FeS2 hollow sphere@graphene microstructure obtained according to the above preparation method.

[0025] A third aspect of the present invention provides an application of FeS2 hollow spheres@graphene microstructures in the negative electrode of potassium-ion batteries.

[0026] Compared with the prior art, the present invention has the following technical effects:

[0027] (1) The method for preparing FeS2 hollow spheres@graphene microstructure provided by the present invention realizes a tightly connected FeS2 hollow spheres@graphene microstructure through the self-polymerization of dopamine and the electrostatic interaction between dopamine and graphene oxide. The preparation process is controllable and is beneficial to the directional preparation of FeS2 anode materials.

[0028] (2) The tightly connected FeS2 hollow spheres@graphene microstructure provided by this invention enhances the interaction between the FeS2 hollow spheres and graphene, accelerating electron transport and improving the structural stability of the FeS2 hollow spheres. In contrast, the loose FeS2 hollow spheres@graphene microstructure control group without dopamine has a weak van der Waals force between the Fe precursor and graphene. Even with the introduction of positively charged groups on the Fe-alcohol complex, the interaction between the material and graphene oxide remains weak, resulting in a loose structure with poor uniform loading. This loose structure leads to poor electronic conductivity and structural stability. The FeS2 hollow spheres without any coating exhibit even worse electronic conductivity and structural stability.

[0029] (3) The tightly connected FeS2 hollow spheres@graphene microstructure provided by the present invention has excellent rate performance and excellent cycle stability when applied to the negative electrode of potassium-ion batteries; the potassium-ion battery assembled with Prussian blue as the positive electrode also has good performance. Attached Figure Description

[0030] Figure 1 Electron microscopy images of tightly connected FeS2 hollow spheres@graphene microstructures (ac), loosely connected FeS2 hollow spheres@graphene microstructures (df), and FeS2 hollow sphere microstructures (gi);

[0031] Figure 2 XRD patterns (a) and TGA patterns (b) of tightly connected FeS2 hollow spheres@graphene, loosely connected FeS2 hollow spheres@graphene, and FeS2 hollow sphere microstructures;

[0032] Figure 3 High-resolution XPS images of tightly connected FeS2 hollow spheres@graphene: Fe 2p (a), S2p (b), C 1s (c);

[0033] Figure 4 A comparison of rate performance for tightly connected FeS2 hollow spheres@graphene, loosely connected FeS2 hollow spheres@graphene, and FeS2 hollow sphere microstructures;

[0034] Figure 5 For tightly connected FeS2 hollow spheres@graphene, loosely connected FeS2 hollow spheres@graphene, and FeS2 hollow sphere microstructures in 1Ag -1 Stability comparison;

[0035] Figure 6 For tightly connected FeS2 hollow spheres@graphene, loosely connected FeS2 hollow spheres@graphene, and FeS2 hollow sphere microstructures in 5Ag -1 Stability comparison;

[0036] Figure 7 EIS plots (a) and corresponding Log(i)-log(v) plots (b) of tightly connected FeS2 hollow spheres@graphene, loosely connected FeS2 hollow spheres@graphene, and FeS2 hollow sphere microstructures at low potential;

[0037] Figure 8 GITT diagrams (a) of tightly connected FeS2 hollow spheres@graphene, loosely connected FeS2 hollow spheres@graphene, and FeS2 hollow sphere microstructures, and the corresponding diffusion coefficients (bc) under the discharge and charge states.

[0038] Figure 9 Rate performance (a) and stability (b) of potassium-ion batteries with tightly connected FeS2 hollow spheres@graphene as the negative electrode and Prussian blue as the positive electrode. Detailed Implementation

[0039] To make the present invention more apparent and understandable, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The embodiments described below are only for explaining the present invention and are not intended to limit the present invention in any form or substance.

[0040] In a first aspect, embodiments of the present invention provide a method for preparing tightly connected FeS2 hollow spheres@graphene microstructures, comprising the following steps:

[0041] S1. Ferric nitrate was added to a mixture of alcohols and stirred. A certain volume of deionized water was added, and the mixture was reacted at a certain temperature for 12 hours to obtain the Fe-alcohol complex. The resulting product was centrifuged, washed several times with ethanol, and dried at 60°C for 12 hours.

[0042] Taking isopropanol and glycerol as examples, in a specific embodiment, isopropanol and glycerol are first mixed at a volume ratio of 7:1 and stirred for 15 minutes to obtain a homogeneous mixed solution with a volume of 60 mL. Ferric nitrate nonahydrate is added to the mixed solution and stirred continuously for 15 minutes. Then, 1.5% by volume of deionized water is added and stirred for 15 minutes. The solution is then transferred to a polytetrafluoroethylene reactor liner and reacted at 190°C for 12 hours. The resulting light green product is centrifuged at 7000 rpm and washed multiple times with ethanol. Finally, it is dried in a vacuum drying oven at 60°C for 12 hours.

[0043] S2. Disperse the product obtained in S1 in a buffer solution (pH=8) and sonicate for 1 hour. Add dopamine hydrochloride to the resulting dispersion while stirring, and continue stirring for a certain period of time. Centrifuge the resulting product and wash with ethanol. After drying at 60°C, add a cationic surfactant solution, sonicate for 1 hour, centrifuge, and wash repeatedly with deionized water.

[0044] In a specific embodiment, approximately 80 mg of the product obtained in step S1 was added to 80 mL of tris(hydroxymethyl)aminomethane buffer solution and ultrasonically dispersed for 1 h. Then, 80 mg of dopamine hydrochloride was added while stirring, and stirring continued for 0.5 h. During this process, the color of the dispersion gradually changed from pale green to brownish-red. After stirring, the product was centrifuged at 7000 rpm and washed with ethanol. After drying in a vacuum drying oven at 60°C, it was added to a 10% (w / w) polydiallyldimethylammonium chloride solution, ultrasonicated for 1 h, centrifuged, and washed repeatedly with deionized water to remove excess surfactant. Finally, it was dried in a vacuum drying oven at 60°C for 12 h.

[0045] S3. Under stirring, add the product obtained in S2 to the graphene oxide dispersion (1 mg / mL) in a certain proportion, stir continuously for 15 min, centrifuge and place the precipitate in a freeze dryer to freeze dry for more than 16 h.

[0046] In a specific embodiment, graphene oxide needs to be prepared first using a modified Hummer's method. 80 mg of graphene oxide is ultrasonically dispersed in 80 mL of deionized water to obtain 1 mg / mL of graphene oxide. -1A graphene oxide dispersion was prepared. 60 mg of the product obtained from S2 was ultrasonically dispersed in 20 mL of deionized water. The product from S2 to graphene oxide was then added to the graphene oxide dispersion under stirring, at a mass ratio of 1.5:2. During this process, rapid electrostatic self-assembly occurred, and the dispersion turned grayish-green. Stirring was continued for 15 min to ensure a more uniform material structure. After centrifugation at 8000 rpm, the precipitate was dried at -82℃ for 16 h.

[0047] S4. Place the material obtained in S3 in the central area of ​​a tube furnace and calcine it at a certain temperature for 3 hours. After cooling to room temperature, mix the sulfur powder with the obtained material in a certain proportion and place it in a tube furnace to calcine at 400°C for 2 hours to obtain the desired material.

[0048] In a specific embodiment, the freeze-dried sample is placed in a quartz boat, which is then positioned in the center of a tube furnace. The tube furnace is completely sealed and evacuated to remove air. When the pressure inside the tube furnace reaches a high vacuum, the argon gas flow valve is opened, allowing argon gas to flow into the furnace at a rate of 40 sccm. A rubber hose connects the outlet of the tail valve of the tube furnace to the sealing water. Once the pressure inside the tube furnace returns to slightly above atmospheric pressure, the downstream gas valve is opened, allowing the argon gas to flow evenly into the water. The water acts as a barrier to isolate the furnace from external air during this process. The heating rate of the tube furnace is set to 2°C / min. -1 The initial temperature was 20℃, and the final calcination temperature was 500℃. After reaching the final temperature, the sample was held for 3 hours. After cooling to room temperature, the sample was removed and mixed with sulfur powder at a sulfur powder to material mass ratio of 5:1. The mixture was then placed back into a quartz boat and sealed in a tube furnace, where the same vacuuming and argon gas purging procedures were performed. However, the holding temperature was set to 400℃ for 2 hours, and the argon gas flow rate was adjusted to 20 sccm during the heating process to reduce sulfur loss.

[0049] Secondly, this invention provides a method for preparing tightly connected FeS2 hollow spheres@graphene microstructures for use as a negative electrode in high-rate potassium-ion batteries. Compared to loosely connected FeS2 hollow spheres@graphene and FeS2 hollow sphere microstructures, the tightly connected FeS2 hollow spheres@graphene microstructures prepared by this invention have a denser FeS2 hollow sphere-graphene interface, and their advantages are mainly reflected in: 1) significantly improved electrical conductivity of the material, and 2) significantly improved structural stability of the material.

[0050] Thirdly, embodiments of the present invention provide a potassium-ion battery anode containing a tightly connected FeS2 hollow sphere@graphene micron structure.

[0051] Fourthly, embodiments of this application provide a potassium-ion battery device comprising the aforementioned tightly connected FeS2 hollow spheres@graphene micron-structured negative electrode and Prussian blue positive electrode.

[0052] The technical solutions of this application will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0053] Example 1

[0054] Isopropanol and glycerol were mixed and stirred at a volume ratio of 7:1 to obtain a homogeneous solution. Ferric nitrate nonahydrate was added to the solution and stirred. Deionized water was added at 1.5% of the solution volume. The mixture was reacted at 190°C for 12 hours. The precipitate was centrifuged and washed with ethanol. The precipitate was then dried under vacuum at 60°C.

[0055] Take approximately dried sample and add it to tris(hydroxymethyl)aminomethane buffer solution. Disperse by sonication. Add an appropriate amount of dopamine hydrochloride at a mass ratio of sample to dopamine hydrochloride of 1:1 and stir for 0.5 h. Centrifuge and wash with ethanol. Dry under vacuum at 60 °C. Add 10% polydiallyldimethylammonium chloride solution, sonicate, centrifuge, wash thoroughly with deionized water, and dry under vacuum.

[0056] After preparing graphene oxide using a modified Hummer's method, the graphene oxide was ultrasonically dispersed in deionized water to obtain 1 mg / mL. -1 Uniform graphene oxide dispersion. Vacuum-dried samples were ultrasonically dispersed in deionized water. The sample dispersion was added to the graphene oxide dispersion at a mass ratio of 1.5:2, and stirred for 15 min. After centrifugation, the precipitate was freeze-dried for 16 h.

[0057] The freeze-dried sample was calcined at 500℃ in an argon atmosphere for 3 hours. After cooling to room temperature, sulfur powder was added at a mass ratio of sulfur powder to material of 5:1 and mixed evenly. The sample was then calcined again at 400℃ in an argon atmosphere for 2 hours.

[0058] Example 2

[0059] Isopropanol and glycerol were mixed and stirred at a volume ratio of 7:1 to obtain a homogeneous solution. Ferric nitrate nonahydrate was added to the solution and stirred. Deionized water was added at 1.5% of the solution volume. The mixture was reacted at 190°C for 12 hours. The precipitate was centrifuged and washed with ethanol. The precipitate was then dried under vacuum at 60°C.

[0060] Take approximately dried sample and add it to tris(hydroxymethyl)aminomethane buffer solution, sonicate to disperse, add an appropriate amount of dopamine hydrochloride at a mass ratio of sample to dopamine hydrochloride of 2:1, stir for 2 hours. Centrifuge and wash with ethanol, vacuum dry at 60℃, add 10% sodium dodecylbenzenesulfonate solution, sonicate, centrifuge and wash thoroughly with deionized water, vacuum dry;

[0061] After preparing graphene oxide using a modified Hummer's method, the graphene oxide was ultrasonically dispersed in deionized water to obtain 1 mg / mL. -1 Uniform graphene oxide dispersion. Vacuum-dried samples were ultrasonically dispersed in deionized water. The sample dispersion was added to the graphene oxide dispersion at a mass ratio of 1:2, and stirred for 15 min. After centrifugation, the precipitate was freeze-dried for 16 h.

[0062] The freeze-dried sample was calcined at 500℃ in an argon atmosphere for 3 hours. After cooling to room temperature, sulfur powder was added at a mass ratio of sulfur powder to material of 5:1 and mixed evenly. The sample was then calcined again at 400℃ in an argon atmosphere for 2 hours.

[0063] Example 3

[0064] Isopropanol and glycerol were mixed and stirred at a volume ratio of 7:1 to obtain a homogeneous solution. Ferric nitrate nonahydrate was added to the solution and stirred. Deionized water was added at 1.5% of the solution volume. The mixture was reacted at 190°C for 12 hours. The precipitate was centrifuged and washed with ethanol. The precipitate was then dried under vacuum at 60°C.

[0065] Take approximately dried sample and add it to tris(hydroxymethyl)aminomethane buffer solution. Disperse by sonication. Add an appropriate amount of dopamine hydrochloride at a mass ratio of sample to dopamine hydrochloride of 1:1 and stir for 0.5 h. Centrifuge and wash with ethanol. Dry under vacuum at 60 °C. Add 10% polydiallyldimethylammonium chloride solution, sonicate, centrifuge, wash thoroughly with deionized water, and dry under vacuum.

[0066] After preparing graphene oxide using a modified Hummer's method, the graphene oxide was ultrasonically dispersed in deionized water to obtain 1 mg / mL. -1 Uniform graphene oxide dispersion. Vacuum-dried samples were ultrasonically dispersed in deionized water. The sample dispersion was added to the graphene oxide dispersion at a mass ratio of 1.5:2, and stirred for 15 min. After centrifugation, the precipitate was freeze-dried for 16 h.

[0067] The freeze-dried sample was calcined at 550℃ in an argon atmosphere for 3 hours. After cooling to room temperature, sulfur powder was added at a mass ratio of 1:1 to the material and mixed evenly. The sample was then calcined again at 400℃ in an argon atmosphere for 2 hours.

[0068] Example 4

[0069] Isopropanol and glycerol were mixed and stirred at a volume ratio of 7:1 to obtain a homogeneous solution. Ferric nitrate nonahydrate was added to the solution and stirred. Deionized water was added at 1.5% of the solution volume. The mixture was reacted at 190°C for 12 hours. The precipitate was centrifuged and washed with ethanol. The precipitate was then dried under vacuum at 60°C.

[0070] Take approximately dried sample and add it to tris(hydroxymethyl)aminomethane buffer solution. Disperse by sonication. Add an appropriate amount of dopamine hydrochloride at a mass ratio of sample to dopamine hydrochloride of 1:1 and stir for 0.5 h. Centrifuge and wash with ethanol. Dry under vacuum at 60 °C. Add 10% polydiallyldimethylammonium chloride solution, sonicate, centrifuge, wash thoroughly with deionized water, and dry under vacuum.

[0071] After preparing graphene oxide using a modified Hummer's method, the graphene oxide was ultrasonically dispersed in deionized water to obtain 1 mg / mL. -1 Uniform graphene oxide dispersion. Vacuum-dried samples were ultrasonically dispersed in deionized water. The sample dispersion was added to the graphene oxide dispersion at a mass ratio of 1.5:2, and stirred for 15 min. After centrifugation, the precipitate was freeze-dried for 16 h.

[0072] The freeze-dried sample was calcined at 450℃ in an argon atmosphere for 5 hours. After cooling to room temperature, sulfur powder was added at a mass ratio of sulfur powder to material of 3:1 and mixed evenly. The sample was then calcined again at 400℃ in an argon atmosphere for 2 hours.

[0073] Comparative Example 1

[0074] Isopropanol and glycerol were mixed and stirred at a volume ratio of 7:1 to obtain a homogeneous solution. Ferric nitrate nonahydrate was added to the solution and stirred. Deionized water was added at 1.5% of the solution volume. The mixture was reacted at 190°C for 12 hours. The precipitate was centrifuged and washed with ethanol. The precipitate was then dried under vacuum at 60°C.

[0075] After preparing graphene oxide using a modified Hummer's method, the graphene oxide was ultrasonically dispersed in deionized water to obtain 1 mg / mL. -1 Uniform graphene oxide dispersion. Vacuum-dried samples were ultrasonically dispersed in deionized water. The sample dispersion was added to the graphene oxide dispersion at a mass ratio of 1.5:2, and stirred for 15 min. After centrifugation, the precipitate was freeze-dried for 16 h.

[0076] The freeze-dried sample was calcined at 500℃ in an argon atmosphere for 3 hours. After cooling to room temperature, sulfur powder was added at a mass ratio of sulfur powder to material of 5:1 and mixed evenly. The sample was then calcined again at 400℃ in an argon atmosphere for 2 hours.

[0077] Comparative Example 2

[0078] Isopropanol and glycerol were mixed and stirred at a volume ratio of 7:1 to obtain a homogeneous solution. Ferric nitrate nonahydrate was added to the solution and stirred. Deionized water was added at 1.5% of the solution volume. The mixture was reacted at 190°C for 12 hours. The precipitate was centrifuged and washed with ethanol. The precipitate was then dried under vacuum at 60°C.

[0079] The sample was calcined at 500℃ in an argon atmosphere for 3 hours. After cooling to room temperature, sulfur powder was added at a mass ratio of sulfur powder to material of 5:1 and mixed evenly. The sample was then calcined again at 400℃ in an argon atmosphere for 2 hours.

[0080] Application examples

[0081] Electrode preparation method: The sample, conductive carbon black (super P), and polyvinylidene fluoride (PVDF) were uniformly dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1, stirred into a uniform slurry, coated on copper foil (9 μm thick), and vacuum dried for 12 h.

[0082] The electrodes prepared from the materials obtained in Example 1 and Comparative Examples 1-2 were perforated into circular electrode sheets with a diameter of 11 mm, and the surface loading of the active material was 1 mg / cm². -2 A CR2032 battery was assembled in an argon glove box using an electrode sheet as the working electrode, potassium metal as the counter electrode and reference electrode, 2M KFSI / DME as the electrolyte, and Whatman glass fiber as the separator.

[0083] The assembled half-cells were subjected to galvanostatic charge-discharge (GCD), galvanostatic intermittent titration (GITT), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests using a galvanostatic charge-discharge tester (LAND CT2021A) and an Autolab electrochemical workstation (PGSTAT302N). The test voltage range was 0.01–3 V vs. K. + / K. Its capacity, rate performance, cycle stability, ion diffusion coefficient, and impedance characteristics were obtained, and the test results are shown in Table 1 and... Figure 4 As shown:

[0084] Table 1. Capacity and rate performance of the examples and comparative examples.

[0085]

[0086] As shown in the table above, the potassium-ion battery anode prepared by the tightly connected FeS2 hollow spheres@graphene microstructure provided in Example 1 has higher capacity and rate performance than the potassium-ion battery anodes prepared in other examples. Furthermore, its rate performance is even more superior compared to the comparative examples, increasing from 0.4% in Comparative Example 2 and 4.2% in Comparative Example 1 to 41.1% in Example 1. This indicates that the tightly connected FeS2 hollow spheres@graphene microstructure prepared by the method in Example 1 possesses excellent rate performance.

[0087] Table 2 shows the conductivity data for the examples and comparative examples. The conductivity data of the materials under various pressures could be measured using the four-probe method. As can be seen from the data in the figure, Example 1 has considerable conductivity, with conductivity values ​​at all pressures significantly greater than those of Comparative Examples 1 and 2. For Examples 2 and 3, the higher carbon content or calcination temperature resulted in relatively higher conductivity values, but the higher carbon content led to lower capacity and rate performance, and the higher temperature resulted in an impure crystal phase, failing to yield the desired FeS2. For Example 4, a lower first calcination temperature also produced FeS2, but its conductivity was relatively lower than that of Example 1, thus Example 1 better meets the requirements.

[0088] Table 2 Conductivity analysis of the examples and comparative examples

[0089]

[0090] Figure 1 SEM and TEM images of Example 1 and Comparative Examples 1-2 are shown: Figure 1 In this context, ac represents a tightly connected FeS2 hollow sphere@graphene micron structure (denoted as C-HS-FeS2@rGO). Figure 1 In this context, df represents porous FeS2 hollow spheres@graphene (denoted as HS-FeS2@rGO) and Figure 1 The gi in the figure represents the FeS2 hollow sphere microstructure (denoted as HS-FeS2). All three samples contain micron-sized FeS2 hollow spheres, and the tightly connected FeS2 hollow sphere@graphene microstructure exhibits a more compact connection, relying on the dual role of dopamine-derived carbon. On the one hand, it grows on the surface of the Fe-alcohol complex; on the other hand, it forms a compact structure through electrostatic interactions and graphene oxide interactions. This structure is strengthened during subsequent calcination. In contrast, the loose FeS2 hollow sphere@graphene only shows incomplete coating, mainly because the interaction between the Fe-alcohol complex, cationic surfactant, and graphene oxide is weak, resulting in the inability to achieve uniform and compact connections. The FeS2 hollow sphere microstructure shows a more ideal hollow sphere structure formation. High-resolution TEM structures show that all three samples exhibit the typical FeS2 crystal plane (200), indicating that all three materials are FeS2, i.e., pyrite.

[0091] Figure 2 The XRD patterns of Example 1 and the comparative example are shown. Figure 2 a) and TGA diagram ( Figure 2As shown in b), compared with the standard card PDF#42-1340, all three materials exhibit typical FeS2 characteristic peaks, further proving the successful preparation of pure FeS2 materials. The corresponding peaks in Example 1 and Comparative Example 1 are weaker than those in Comparative Example 2 due to the carbon coating effect, which weakens the diffraction of the FeS2 peaks. Thermogravimetric analysis (TGA) calculated the FeS2 content in Example 1 and Comparative Example 1, indicating that the introduction of the intermediate carbon layer increases the carbon content, thus reducing the amount of FeS2 component in the material, corresponding to its relatively lower specific capacity. However, regardless of the actual FeS2 component content in the material (mass fraction 53%) or the capacity of Example 1 (~500 mA hg), the specific capacity remains the same. -1 The values ​​are already quite high. In summary, Example 1 provides a compromise solution that balances the capacity and rate performance of FeS2.

[0092] Figure 3 The image shows the XPS pattern of the material obtained in Example 1, namely the tightly connected FeS2 hollow spheres@graphene micron structure. As can be seen from the figure, the high-resolution spectrum of Fe 2p (…) Figure 3 a) in the text represents Fe 2+ and Fe 3+ 2p 3 / 2 and 2p 1 / 2 Peak, in which Fe 2+ and Fe 3+ These correspond to the Fe-S bonds in FeS2 and the Fe-O bonds in Fe2O3, respectively. Therefore, Fe 2p indicates the successful preparation and partial oxidation of FeS2 materials. The high-resolution spectrum of S2p (…) Figure 3 b) in the figure shows the 2p of the Fe-S bond. 3 / 2 and 2p 1 / 2 The peak also confirmed the 2p of the CSC bond. 3 / 2 and 2p 1 / 2 The peak indicates that, on the one hand, S forms FeS2 with Fe, and on the other hand, it participates in bonding with carbon, i.e., it dopes the carbon component. This is more clearly shown in the high-resolution C1s spectrum. C1s spectrum ( Figure 3 c) in the figure shows the formation of CS bonds, as well as CN bonds, due to the introduction of nitrogen into the carbon material during the decomposition of dopamine and polydiallyldimethylammonium chloride. The introduction of S and N elements will help improve the capacity and rate performance of Example 1.

[0093] Figure 4 The comparison of the rate performance of Example 1 and the comparative example is shown. It can be seen that although Example 1 exhibits a relatively small current, its rate performance is much better than that of the comparative example, which confirms the feasibility of the structure proposed by this method for improving the rate performance of micron-sized FeS2 materials.

[0094] Figure 5 and Figure 6 The cycling capacity changes of Example 1 and Comparative Examples 1-2 at current densities of 1 Ag⁻¹ and 5 Ag⁻¹ are shown respectively. It can be seen that the stability obtained in Example 1 is much higher than that in the comparative examples, indicating that the tightly connected structure is more conducive to the structural stability of micron-sized FeS₂, thus enabling the material to achieve excellent cycle life.

[0095] Figure 7 The EIS test results of Example 1 and Comparative Examples 1-2 at low voltage are shown. Figure 7 In the figure, 'a' represents the EIS plot. Figure 7 In the figure, b represents the Log(i)-log(v) plot. In the high and mid-frequency regions, the tightly connected FeS2 hollow spheres@graphene microstructure exhibits lower charge transfer impedance compared to the loosely connected FeS2 hollow spheres@graphene and FeS2 hollow sphere microstructures. In the low-frequency region, the tightly connected FeS2 hollow spheres@graphene microstructure shows a steeper curve, indicating that Example 1 has lower ion transport resistance.

[0096] Figure 8 The GITT test results of Example 1 and Comparative Examples 1-2 are shown. Figure 8 In the diagram, 'a' represents the GITT plot. Figure 8 (where bc represents the diffusion coefficient under the corresponding discharge and charge states). It can be seen that the tightly connected FeS2 hollow spheres@graphene microstructures exhibit higher ion diffusion coefficients during charge and discharge. This result further explains the higher rate performance of Example 1.

[0097] Figure 9 This demonstrates the rate capability of a potassium-ion battery assembled with the material obtained in Example 1 and Prussian blue as the positive electrode. Figure 9 a) and stability ( Figure 9 (b) in the middle. Figure 9 The potassium-ion battery assembled by this method exhibits good rate performance and stability, further demonstrating that the tightly connected FeS2 hollow spheres@graphene microstructure proposed in this paper has the practical potential to serve as the anode of potassium-ion batteries.

[0098] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a tightly connected iron disulfide hollow sphere@graphene microstructure, characterized in that, The preparation method includes the following steps: S1. A Fe-alcohol complex is obtained by mixing ferric nitrate and alcohol and reacting them. S2. Add dopamine hydrochloride to the Fe-alcohol complex and stir to carry out the polymerization reaction; after the polymerization reaction, add a cationic surfactant. S3. Add the product obtained in S2 to the graphene oxide dispersion and stir to react; S4. The product obtained in S3 is calcined for the first time, and sulfur powder is added for the second calcination to obtain a tightly connected FeS2 hollow sphere@graphene micron structure.

2. The method for preparing the tightly connected iron disulfide hollow spheres@graphene microstructure according to claim 1, characterized in that, In step S1, the ferric nitrate is one of ferric nitrate nonahydrate or ferric nitrate hexahydrate; the alcohol is selected from isopropanol, glycerol or ethylene glycol.

3. The method for preparing the tightly connected iron disulfide hollow sphere@graphene microstructure according to claim 1, characterized in that, In step S1, the reaction temperature is 150–190°C.

4. The method for preparing the tightly connected iron disulfide hollow sphere@graphene microstructure according to claim 1, characterized in that, In step S2, the mass ratio of dopamine hydrochloride to Fe-alcohol complex is 1:1 to 2:1, and the stirring time is 0.5 to 2 hours.

5. The method for preparing the tightly connected iron disulfide hollow sphere@graphene microstructure according to claim 1, characterized in that, In step S2, the cationic surfactant is selected from sodium dodecylbenzenesulfonate or polydiallyldimethylammonium chloride.

6. The method for preparing the tightly connected iron disulfide hollow sphere@graphene microstructure according to claim 1, characterized in that, In step S3, the mass ratio of the product obtained in S2 to graphene oxide is 1:2 to 2:

1.

7. The method for preparing the tightly connected iron disulfide hollow spheres@graphene microstructure according to claim 1, characterized in that, In step S4, the temperature of the first calcination is 450–550°C.

8. The method for preparing the tightly connected iron disulfide hollow sphere@graphene microstructure according to claim 1, characterized in that, In step S4, the mass ratio of the sulfur powder to the product after the first calcination is 1:1 to 5:1; the temperature of the second calcination is 350 to 400°C.

9. A tightly connected FeS2 hollow sphere@graphene microstructure obtained by the preparation method according to any one of claims 1-8.

10. The application of the tightly connected FeS2 hollow spheres@graphene microstructure of claim 9 in the anode of a potassium-ion battery.

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