An iron oxide-cerium oxide composite material, a preparation method and applications thereof

Abstract

The present application relates to a kind of iron oxide-cerium oxide composite material and its preparation method and application, including after etching Fe3O4@C in alkaline environment coating rare earth element, by controlling the difference of reaction step preparation cerium oxide distribution site, and heterojunction series catalytic interface optimization " yolk-egg shell " nanostructure iron oxide-cerium oxide composite material.The present application utilizes the rare earth element Ce with electron-rich 4f inner valence orbit, f orbit electron spin leads to the increase of electron state near dxz / yz, enhances the π bond formed by dxz / yz and px / y hybridization, promotes d-p hybridization, d orbit and p orbit overlap maximum when interacting with LiPSs.f-d-p orbit coupling, f-d-p hybridization is generated when interacting with LiPSs, 4f orbit is activated, plays a catalytic role, improves reaction activity, so that the composite material is used in lithium-sulfur battery has high reversible capacity, good rate performance, long cycle life and competitive area capacity under high sulfur loading.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium-sulfur batteries, in particular to an iron oxide-cerium oxide composite material and a preparation method and application thereof. BACKGROUND

[0002] Achieving the vision of "carbon neutralization" poses new challenges to the efficient collection, storage, conversion and use of energy. In the past three decades, lithium-ion batteries have played a key role in driving innovation in the field of portable electronic devices and electric vehicles. However, the limitations of its energy density have become increasingly apparent, making it difficult to meet the urgent needs of current social rapid development. Lithium-sulfur batteries are considered the most promising candidate for the next generation of high-performance secondary batteries due to their excellent theoretical energy density, abundant sulfur resource reserves and green environmental protection.

[0003] Although lithium-sulfur batteries show broad application prospects, the practical application of lithium-sulfur batteries still faces challenges. Specifically, the problems existing in the sulfur positive electrode include insufficient conductivity, significant volume expansion, "shuttle" behavior of polysulfides and slow conversion reaction kinetics, which together lead to a decrease in the effective utilization rate of active materials, low coulombic efficiency and rapid capacity decay. In addition, the growth of lithium dendrites on the negative electrode also poses a serious safety hazard to the battery.

[0004] Current research on catalysts mainly focuses on optimizing energy levels to promote the adsorption and catalytic conversion of LiPSs, often ignoring the influence of electronic spin state on charge transfer and orbital interaction. The catalytic performance is influenced by factors such as the electronic structure, orbital structure, atomic diameter and loading of the central atom. Most single-atom catalysts are composed of 3d, 4d, 5d and p-block metals.

[0005] The iron oxide-cerium oxide composite has a "yolk-eggshell" structure nanoreactor with an iron oxide core and a conductive carbon shell. The core-shell structure with decreasing adsorption capacity of LiPSs from the inside out is more effective in limiting the diffusion of polysulfides and regulating the deposition of LiPSs.

[0006] Therefore, there is an urgent need to develop a preparation method for an iron oxide-cerium oxide composite material with high product purity, which utilizes the unique electronic structure, 4f valence orbitals and unsaturated coordination environment of rare earth (RE) elements, as well as the "yolk-eggshell" nanoreactor, to enhance the reaction activity and selectivity of the catalyst, in order to realize commercialization of lithium-sulfur batteries. SUMMARY

[0007] Based on this, the purpose of the present application is to provide a preparation method of iron oxide-cerium oxide composite material, which has simple steps and mild conditions, can obtain iron oxide-cerium oxide composite material with different morphologies and crystal structures by accurately controlling the reaction conditions, and the target product is uniformly dispersed and has regular morphology.

[0008] Another purpose of the present application is to provide an iron oxide-cerium oxide composite material which is uniformly dispersed, has regular core-shell structure morphology, exhibits excellent electrochemical performance, and can be well applied to lithium-sulfur batteries; and has obvious interface effect, and the catalyst exhibits synergistic catalytic performance in lithium-sulfur batteries.

[0009] Still another purpose of the present application is to provide an application of the iron oxide-cerium oxide composite material in lithium-sulfur batteries.

[0010] The present inventors found that the iron oxide-cerium oxide composite used in the catalytic reaction in lithium-sulfur batteries can produce synergistic catalytic effect and enhance the reaction activity, and therefore developed a method for preparing iron oxide-cerium oxide composite which can be applied to commercial production, and has simple preparation process, low cost and excellent product performance.

[0011] The present application adopts the following technical solutions:

[0012] A preparation method of iron oxide-cerium oxide composite material, comprising the following steps:

[0013] S1: dissolving a soluble iron salt in ultrapure water, and then adjusting the pH value;

[0014] S2: placing the solution obtained in step S1 in a reaction kettle, and after high-temperature reaction, centrifugal washing and drying;

[0015] S3: dissolving the product of step S2 in a weak alkali solution, adding a dopamine hydrochloride solution, stirring, centrifugal washing and drying;

[0016] S4: high-temperature calcining the product of step S3 to obtain an intermediate product I;

[0017] S5: dissolving an inorganic acid in ultrapure water, adding the intermediate product I for stirring, centrifugal washing and drying to obtain an intermediate product II;

[0018] S6: dispersing and reacting the intermediate product II, cerium salt and alkaline solution in an ultrapure water and ethanol mixed solvent to obtain a mixed solution;

[0019] S7: transferring the mixed solution into a reaction container, and after reaction at 100-400 DEG C, centrifugal washing and drying, a near-final product is obtained.

[0020] S8: Calcining the near-final product in a tube furnace at 350-600 DEG C for 2-4 h.

[0021] The preparation method of the iron oxide-cerium oxide composite material provided by the application can obtain iron oxide-cerium oxide composite materials with different morphologies and crystal structures by precisely adjusting the reaction conditions in each step, and the iron oxide-cerium oxide composite materials highlight different performances, the preparation process is simple to operate, the experimental reproducibility is very good, the cost is low, and the iron oxide-cerium oxide composite material is easy to mass produce. And the iron oxide-cerium oxide composite material prepared by the method has obvious interface effect, and as a catalyst, it shows synergistic catalytic performance in lithium-sulfur batteries.

[0022] Further, the soluble iron salt in step S1 is selected from one or more of ferric chloride, ferric nitrate and ferric sulfate.

[0023] Further, in step S1, the pH value is adjusted by using an inorganic base.

[0024] Further, in step S1, by controlling different pH values, different morphologies of the product can be obtained after high-temperature reaction in step S2.

[0025] Specifically, in step S1, the pH range is adjusted to 8≤pH≤10, and the product obtained in step S2 is a cubic morphology; in step S1, the pH range is adjusted to 10

[0026] Further, in step S2, the high-temperature reaction conditions are: reacting in a reaction kettle at 100-130 DEG C for 36-60 h; and Fe2O3 is obtained after the reaction is completed.

[0027] Further, in step S3, the weak base solution is one or more of Tris, tris-hydroxymethyl aminomethane, aminoacetic acid, diaminoglycollic acid, 4-aminobenzoic acid, amino acid buffer, and N-hydroxyethylpiperazine-N'-ethanesulfonic acid.

[0028] Further, in step S4, the product obtained in step S3 is calcined in a high-temperature furnace at 550-700 DEG C for 2 h, and the obtained intermediate product I is Fe3O4@C.

[0029] Further, in step S5, the inorganic acid is one or more of hydrochloric acid, sulfuric acid and nitric acid, and the inorganic acid is preferably hydrochloric acid.

[0030] Further, in step S5, the intermediate product II obtained by etching with the inorganic acid is a hollow Fe3O4@C cubic structure.

[0031] Further, the alkaline solution in step S6 is selected from one or more of urea, sodium hydroxide, potassium hydroxide, ammonia, and hexamethylenetetramine. Preferably, the alkaline solution is hexamethylenetetramine.

[0032] Further, in step S6, the dispersion of the solution can be stirring dispersion or ultrasonic dispersion.

[0033] Specifically, the alkaline solution is hexamethylenetetramine, and the cerium salt is added and stirred and dispersed. The iron oxide-cerium oxide composite material is in a "yolk-eggshell" structure, and the CeO2 is in a nanosheet shape grown on the surface and in the core of Fe3O4. The nanosheet-shaped cerium oxide structure provides a larger specific surface area, which helps the rapid diffusion and reaction of lithium ions and improves the rate performance of the battery. Due to the superposition between the nanosheets, a good conductive network is formed, which can effectively improve the current transmission efficiency.

[0034] Specifically, the alkaline solution is hexamethylenetetramine, and the cerium salt is added and ultrasonically dispersed. The iron oxide-cerium oxide composite material is in a "yolk-eggshell" structure, and the CeO2 is in a nanoparticle shape grown on the surface and in the core of Fe3O4. The CeO2 nanoparticle doped carbon nanobox can spatially limit and chemically capture LiPSs to reduce the shuttling effect, and has good dispersibility, which is conducive to improving the uniformity of the composite material and enhancing the overall performance of the battery.

[0035] Further, the cerium salt in step S6 is selected from one or more of cerium chloride, cerium nitrate, cerium acetate, and cerium sulfate.

[0036] Further, the intermediate product II in step S6 is a hollow structure containing Fe3O4; and in step S6, the structure and morphology of the reaction product can be controlled by adjusting the molar ratio of Fe3O4 to cerium salt.

[0037] Specifically, the molar ratio of Fe3O4 to cerium salt is (1-20):1, and an iron oxide-cerium oxide composite material with different distribution sites of cerium oxide is obtained. The molar ratio of Fe3O4 to cerium salt is 1:(2-20), and Ce penetrates into the yolk Fe3O4 structure, and after subsequent calcination, a Fe3O4-CeO2@C or Fe2O3-Ce2O3@C tandem catalytic type heterojunction is obtained.

[0038] Further, in step S6, the ratio of the mixed solvent of ultrapure water and ethanol is (1-5):1, which controls the size of the CeO2 particles and the uniform distribution of CeO2 in the iron oxide-cerium oxide composite material of Fe3O4@C.

[0039] Further, in step S7, the structure of the product can be further controlled by controlling the reaction temperature of the hydrothermal reaction.

[0040] Specifically, the hydrothermal reaction is carried out at 200-300 DEG C to form an ordered structure and grow into a nanorod in contact with a nanocore. The introduction of cerium element controls the growth of the crystal, improves the dispersity and uniformity of the material, and improves the reaction activity.

[0041] Specifically, the hydrothermal reaction is carried out at 301-400 DEG C to form an ellipse in contact with a nanocore, and partial mutual reaction occurs, resulting in closer combination and enhanced stability and catalytic performance of the material.

[0042] Further, the crystal structure of the product is controlled by controlling the calcination temperature in step S8.

[0043] Specifically, when 350 DEG C <= calcination temperature <= 450 DEG C, the oxide of iron is Fe3O4, and the oxide of cerium is CeO2. When 450 DEG C < calcination temperature <= 600 DEG C, Fe3O4 changes to alpha-Fe2O3, the morphology changes from nanoparticles to porous, CeO2 changes to Ce2O3, and the particle size can be accurately controlled by the reaction conditions.

[0044] The beneficial effects of the present application are:

[0045] (1) The purpose of the present application is to solve the problems of low capacity and poor cycle stability of current lithium-sulfur batteries, and a new process for preparing a "yolk-eggshell" structure iron oxide-cerium oxide composite material is proposed. By compounding the iron oxide and the cerium oxide, the cerium is a rare earth element, 4f x 5d y 6s valence electron configuration, f-d-p orbital coupling, when interacting with LiPSs, f-d-p hybridization is generated, the closed and inactive 4f orbit is activated, providing abundant channels and spaces for ion diffusion and electrolyte flow; the special valence electron structure and large atomic radius form a higher coordination number, producing strong substrate anchoring effect and larger electronic delocalization effect. The nature of the rare earth valence shell 4f orbit (high degeneracy and locality) provides more spin-orbit coupling than d orbit. The rare earth and the coordination atom form a local "electron transfer bridge" or "electron storage station" through the rich spin-orbit coupling, activate the adsorbate to promote the subsequent catalytic conversion reaction.

[0046] (2) The preparation method of the present application is simple, inorganic acid etching Fe3O4@C is selected, the reaction rate and internal core in the synthesis process are accurately controlled, the "yolk-eggshell" structure with LiPSs adsorption gradient is designed, the area / volume load of sulfur is increased, the use rate of electrolyte is reduced, and the utilization rate of sulfur is increased, so as to further improve the volume energy / power density of Li-S battery.

[0047] (3) The iron oxide-cerium oxide composite material is successfully prepared by a simple hydrothermal synthesis method and post-calcination.

[0048] (4) The "yolk-eggshell" nanoreactor prepared by the application provides a volume buffer cavity as an active center container through the "cavity" structure combined with cerium elements; the "yolk" active center is designed to improve catalytic conversion and accelerate reaction kinetics; the microenvironment formed by flexible active sites and rich molecular diffusion paths regulates the conversion of sulfur substances in a specific nanoscale range, and provides rich channels and spaces for ion diffusion and electrolyte flow.

[0049] (5) The cerium oxide nanostructure closely grown on the surface of the iron oxide forms rich nanointerfaces and ensures strong chemical interaction between metals.

[0050] (6) The iron oxide-cerium oxide composite material prepared by the application can be well applied to lithium-sulfur batteries, has obvious interface effects, and exhibits synergistic catalytic performance as a catalyst in lithium-sulfur batteries.

[0051] In order to better understand and implement, the application is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 The XRD pattern of the iron oxide-cerium oxide composite material prepared for Example 1;

[0053] Figure 2-a The TEM pattern of the iron oxide-cerium oxide composite material prepared for Example 1;

[0054] Figure 2-b The TEM pattern of the iron oxide-cerium oxide composite material prepared for Example 2;

[0055] Figure 2-c The TEM pattern of the iron oxide-cerium oxide composite material prepared for Example 3;

[0056] Figure 3 The SEM pattern of the iron oxide-cerium oxide composite material prepared for Example 1;

[0057] Figure 4-a The performance pattern of the iron oxide-cerium oxide composite material prepared for Examples 1-2 at 0.5C;

[0058] Figure 4-bPerformance graph of the iron oxide-cerium oxide composite material prepared for Examples 1-2 at 1C;

[0059] Figure 5-a Performance graph of the iron oxide-cerium oxide composite material prepared for Examples 3-5 at 0.5C;

[0060] Figure 5-b Performance graph of the iron oxide-cerium oxide composite material prepared for Examples 3-5 at 1C. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0062] A preparation method of an iron oxide-cerium oxide composite material, comprising the following steps:

[0063] S1: dissolving a soluble iron salt in ultrapure water, and then adjusting the pH value;

[0064] S2: placing the solution obtained in step S1 in a reaction kettle, and reacting at 100-130°C in the reaction kettle for 36-60h; after the reaction is completed, Fe2O3 is obtained, centrifuged, washed, and dried;

[0065] S3: dissolving the product of step S2 in a weak alkali solution, adding a dopamine hydrochloride solution, stirring, centrifuging, washing, and drying;

[0066] S4: calcining the product of step S3 at 550-700°C in a high-temperature furnace for 2h to obtain intermediate product I Fe3O4@C;

[0067] S5: dissolving an inorganic acid in ultrapure water, adding intermediate product I, stirring, centrifuging, and drying to obtain intermediate product II YS Fe3O4@C;

[0068] S6: weighing intermediate product II, cerium salt, and hexamethylenetetramine in a mixed solvent of ultrapure water and ethanol according to a proportion, stirring or ultrasonically dispersing the solution uniformly, and reacting to obtain a mixed solution;

[0069] S7: transferring the mixed solution into a reaction kettle, reacting at 100-400°C, and then centrifuging, washing with water and ethanol, and drying to obtain a near-final product;

[0070] S8: The near end product is placed in a tube furnace at 400-600℃ for calcination for 2-4h to obtain the target product of iron oxide-cerium oxide composite material catalyst.

[0071] Example 1

[0072] Take 30mL ultrapure water into the inner container, heat to 75℃ in water bath, weigh 16.218g FeCl3·6H2O, add to the inner container, stir for 5min to obtain solution A, weigh a certain amount of NaOH dissolved in ultrapure water to obtain solution B, pour solution B into solution A to adjust pH to 8.25, transfer the obtained solution to the reaction kettle, and react at 110℃ for 48h. After the reaction is completed, the sample is collected, washed with water for 2-3 times, washed with ethanol for 2-3 times, and dried to obtain Fe2O3. Weigh 1g Fe2O3, 0.1214g Tris is dissolved in 100mL ultrapure water to form solution C, 0.6g dopamine hydrochloride is dissolved in 12mL ultrapure water to form solution D, pour solution D into solution C, stir at room temperature for 12h, centrifugal wash and dry. Calcine in a tube furnace at 600℃ for 2h, after the reaction is completed, the sample is collected to obtain Fe3O4@C, hydrochloric acid is added to ultrapure water, the material is added, and etching is carried out at room temperature for 4h to obtain YS Fe3O4@C. Weigh 100mg YS Fe3O4@C, 60mg Ce(NO)3·6H2O and 8mg hexamethylenetetramine, and stir and disperse in 30mL ultrapure water and 30mL ethanol mixed solvent, transfer the obtained solution to the reaction kettle, and react at 100℃ for 10h. After the reaction is completed, the sample is collected, washed with water for 2-3 times, washed with ethanol for 2-3 times, and dried. Calcine in a tube furnace at 400℃ for 3h to obtain the target product of iron oxide-cerium oxide composite material catalyst.

[0073] Example 2

[0074] Take 30 mL of ultrapure water into the inner container, heat to 75°C in water bath, take 16.218 g of FeCl3·6H2O, add to the inner container, stir for 5 min, get solution A, take a certain amount of NaOH dissolved in ultrapure water to get solution B, pour solution B into solution A to adjust pH to 8.25, transfer the obtained solution to the reaction kettle, react at 110°C for 48 h. After the reaction is completed, collect the sample, wash with water for 2-3 times, wash with ethanol for 2-3 times, and dry to obtain Fe2O3. Take 1 g of Fe2O3, 0.1214 g of Tris dissolved in 100 mL of ultrapure water to form solution C, take 0.6 g of dopamine hydrochloride dissolved in 12 mL of ultrapure water to form solution D, pour solution D into solution C, stir at room temperature for 12 h, centrifugal wash, and dry. Calcine in a tube furnace at 600°C for 2 h, after the reaction is completed, collect the sample to obtain Fe3O4@C, add hydrochloric acid into ultrapure water, add the material, etch at room temperature for 4 h to obtain YS Fe3O4@C. Take 100 mg of YS Fe3O4@C, 60 mg of Ce(NO)3·6H2O and 8 mg of hexamethylenetetramine ultrasonic dispersion in 30 mL of ultrapure water and 30 mL of ethanol mixed solvent, transfer the obtained solution to the reaction kettle, react at 100°C for 10 h, after the reaction is completed, collect the sample, wash with water for 2-3 times, wash with ethanol for 2-3 times, and dry. Calcine in a tube furnace at 400°C for 3 h to obtain the target product iron oxide-cerium oxide composite material catalyst.

[0075] Example 3

[0076] Take 30 mL of ultrapure water into the inner container, heat to 75°C in water bath, take 16.218 g of FeCl3·6H2O, add to the inner container, stir for 5 min, get solution A, take a certain amount of NaOH dissolved in ultrapure water to get solution B, pour solution B into solution A to adjust pH to 12, transfer the obtained solution to the reaction kettle, react at 110°C for 48 h. After the reaction is completed, the sample is collected, washed with water for 2-3 times, washed with ethanol for 2-3 times, and dried to obtain Fe2O3. Take 1 g of Fe2O3, 0.1214 g of Tris dissolved in 100 mL of ultrapure water to form solution C, take 0.6 g of dopamine hydrochloride dissolved in 12 mL of ultrapure water to form solution D, pour solution D into solution C, stir at room temperature for 12 h, centrifugal wash, and dry. Calcine in a tube furnace at 600°C for 2 h, after the reaction is completed, collect the sample to obtain Fe3O4@C, add hydrochloric acid to ultrapure water, add the material, and etch at room temperature for 4 h to obtain YS Fe3O4@C. Take 100 mg of YS Fe3O4@C, 44 mg of Ce(NO)3·6H2O and 8 mg of hexamethylenetetramine, and stir and disperse them in a mixed solvent of 30 mL of ultrapure water and 30 mL of ethanol, transfer the obtained solution to the reaction kettle, react at 100°C for 10 h, after the reaction is completed, collect the sample, wash with water for 2-3 times, wash with ethanol for 2-3 times, and dry. Calcine in a tube furnace at 400°C for 3 h to obtain the target product, an iron oxide-cerium oxide composite material catalyst.

[0077] Example 4

[0078] Take 30 mL of ultrapure water into the inner container, heat to 75°C in water bath, take 16.218 g of FeCl3·6H2O, add to the inner container, stir for 5 min, get solution A, take a certain amount of NaOH dissolved in ultrapure water to get solution B, pour solution B into solution A to adjust pH to 8.25, transfer the obtained solution to the reaction kettle, react at 110°C for 48 h. After the reaction is completed, collect the sample, wash with water for 2-3 times, wash with ethanol for 2-3 times, and dry to obtain Fe2O3. Take 1 g of Fe2O3, 0.1214 g of Tris dissolved in 100 mL of ultrapure water to form solution C, take 0.6 g of dopamine hydrochloride dissolved in 12 mL of ultrapure water to form solution D, pour solution D into solution C, stir at room temperature for 12 h, centrifugal wash, and dry. Calcine in a tube furnace at 600°C for 2 h, after the reaction is completed, collect the sample to obtain Fe3O4@C, add hydrochloric acid into ultrapure water, add the material, etch at room temperature for 4 h to obtain YS Fe3O4@C. Take 100 mg of YS Fe3O4@C, 80 mg of Ce(NO)3·6H2O and 8 mg of hexamethylenetetramine, stir and disperse in 30 mL of ultrapure water and 30 mL of ethanol mixed solvent, transfer the obtained solution to the reaction kettle, react at 100°C for 10 h, after the reaction is completed, collect the sample, wash with water for 2-3 times, wash with ethanol for 2-3 times, and dry. Calcine in a tube furnace at 400°C for 3 h to obtain the target product iron oxide-cerium oxide composite material catalyst.

[0079] Example 5

[0080] Take 30 mL of ultrapure water into the inner container, heat to 75°C in water bath, take 16.218 g of FeCl3·6H2O, add to the inner container, stir for 5 min, get solution A, take a certain amount of NaOH dissolved in ultrapure water to get solution B, pour solution B into solution A to adjust pH to 8.25, transfer the obtained solution to the reaction kettle, and react at 110°C for 48h. After the reaction is completed, the sample is collected, washed with water for 2-3 times, washed with ethanol for 2-3 times, and dried to obtain Fe2O3. Take 1 g of Fe2O3, 0.1214 g of Tris dissolved in 100 mL of ultrapure water to form solution C, take 0.6 g of dopamine hydrochloride dissolved in 12 mL of ultrapure water to form solution D, pour solution D into solution C, stir at room temperature for 12h, centrifugal wash, and dry. Calcine in a tube furnace at 600°C for 2h, after the reaction is completed, the sample is collected to obtain Fe3O4@C, hydrochloric acid is added to ultrapure water, the material is added, and etching is carried out at room temperature for 4h to obtain YS Fe3O4@C. Take 100 mg of YS Fe3O4@C, 120 mg of Ce(NO)3·6H2O and 8 mg of hexamethylenetetramine, and stir and disperse them in a mixed solvent of 30 mL of ultrapure water and 30 mL of ethanol, transfer the obtained solution to a reaction kettle, react at 100°C for 10h, after the reaction is completed, the sample is collected, washed with water for 2-3 times, washed with ethanol for 2-3 times, and dried. Calcine in a tube furnace at 400°C for 3h to obtain the target product of the iron oxide-cerium oxide composite material catalyst.

[0081] Performance testing

[0082] The iron oxide-cerium oxide composite material catalyst prepared in Examples 1-5 was subjected to the following performance tests: 1. XRD test

[0083] Figure 1 The XRD test of the iron oxide-cerium oxide composite material prepared in Example 1 was performed. The results showed that the sample was a composite of Fe3O4(JCPDS 19-0629) and CeO2(JCPDS 43-1002).

[0084] 2. TEM test

[0085] Figure 2 is a TEM image of the iron oxide-cerium oxide composite material prepared in Examples 1-3, from which it can be seen that the Fe3O4-CeO2 composite material prepared in Examples 1-3 has a core-shell structure of egg yolk-egg shell with a size of about 500 nm.

[0086] Among them, from Figure 2-a It can be seen that the Fe3O4-CeO2 composite material prepared by stirring and dispersing in Example 1 has a cubic core-shell structure, and the CeO2 is a nanosheet grown on the surface of Fe3O4 and in the core. Figure 2-bIt can be seen that the Fe3O4-CeO2 composite material obtained by ultrasonic dispersion in Example 2 has a cubic core-shell structure, and the CeO2 is a nanoparticle grown on the surface and in the core of Fe3O4. Figure 2-c It can be seen that the Fe3O4-CeO2 composite material obtained by adjusting the pH value of the soluble iron salt solution to 12 in Example 3 has a peanut-like shape.

[0087] 3. SEM test

[0088] Figure 3 The SEM image of the Fe3O4-CeO2 composite material prepared in Example 1. As can be seen from the scanning electron microscope image, the synthesized Fe3O4-CeO2 composite material has a cubic box structure with a size of about 500 nm.

[0089] 4. Battery performance test

[0090] Figure 4 is a performance test diagram of the iron oxide-cerium oxide composite material prepared in Example 1 and Example 2 at 0.5C and 1C. As can be seen from the figure, the iron oxide-cerium oxide composite material obtained by stirring dispersion and the iron oxide-cerium oxide composite material obtained by ultrasonic dispersion can both exhibit excellent electrocatalytic performance. In Example 1, the CeO2 is a nanosheet grown on the surface and in the core of Fe3O4, and the nanosheet-like CeO2 structure provides a large specific surface area, which helps the rapid diffusion and reaction of lithium ions and improves the rate performance of the battery. Due to the superposition between the nanosheets, a good conductive network is formed, which can effectively improve the current transmission efficiency. In Example 2, the CeO2 is a nanoparticle grown on the surface and in the core of Fe3O4, and the CeO2 nanoparticle doped carbon nanobox can spatially limit and chemically capture LiPSs to reduce the shuttle effect, and has good dispersibility, which is beneficial to improve the uniformity of the composite material and enhance the overall performance of the battery.

[0091] Figure 5 is a performance test diagram of the iron oxide-cerium oxide composite material prepared in Examples 3-5 at 0.5C and 1C, and it can be seen that the Fe3O4 and cerium salt molar ratio within a certain range can prepare an iron oxide-cerium oxide composite material with excellent electrocatalytic performance.

[0092] Therefore, the composite material with different morphologies and crystal structures can be obtained by controlling the reaction condition, the oxide of iron is combined with the oxide of cerium to obtain the "yolk-eggshell" nano reactor, the "cavity" structure combined with the cerium element is used as an active center container to provide a volume buffer cavity, the "yolk" active center is designed to improve catalytic conversion and accelerate reaction kinetics, the microenvironment formed by flexible active sites and rich molecular diffusion paths regulates the conversion of sulfur substances in a specific nanometer scale range, and abundant channels and spaces are provided for ion diffusion and electrolyte flow.

[0093] The above-mentioned examples only express several embodiments of the present application, and the description is relatively specific and detailed, but it cannot be understood as the limitation of the scope of the patent right of the present application. It should be pointed out that, for ordinary skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and the present application also intends to include these modifications and improvements.

Claims

1. A method for preparing an iron oxide-cerium oxide composite material, characterized in that: It includes the following steps: S1: Dissolve soluble iron salt in ultrapure water, and then adjust the pH value; S2: Place the solution obtained in step S1 in a reaction kettle, after high-temperature reaction, centrifuge, wash and dry; S3: Dissolve the product of step S2 in a weak base solution, add dopamine hydrochloride solution, stir, then centrifuge, wash and dry; S4: Calcinate the product of step S3 at high temperature to obtain intermediate product I; S5: Dissolve inorganic acid in ultrapure water, add intermediate product I and stir, centrifuge, wash and dry to obtain hollow Fe3O4@C; S6: Disperse hollow Fe3O4@C, cerium salt and selected basic solution in a mixed solvent of ultrapure water and ethanol, after uniform dispersion, react to obtain a mixed solution; S7: Transfer the mixed solution into a reaction vessel, after reaction at 100 - 400 °C, centrifuge, wash and dry to obtain a near-final product; S8: Calcinate the near-final product in a tubular furnace at 350 - 600 °C for 2 - 4 h to obtain an iron oxide-cerium oxide composite material.

2. The preparation method of an iron oxide-cerium oxide composite material according to claim 1, wherein: The soluble iron salt described in step S1 is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate.

3. The preparation method of an iron oxide-cerium oxide composite material according to claim 1, wherein: Adjust the pH range to 8 ≤ pH ≤ 10 in step S1, and the product obtained in step S2 has a cubic morphology; Alternatively, adjust the pH range to 10 < pH ≤ 13 in step S1, and the product obtained in step S2 has a peanut-like morphology.

4. The preparation method of an iron oxide-cerium oxide composite material according to claim 1, wherein: The cerium salt described in step S6 is selected from one or more of cerium chloride, cerium nitrate, cerium acetate, and cerium sulfate.

5. The preparation method of an iron oxide-cerium oxide composite material according to claim 1, wherein: The basic solution described in step S6 is selected from one or more of urea, sodium hydroxide, potassium hydroxide, ammonia water, and hexamethylenetetramine.

6. The preparation method of an iron oxide-cerium oxide composite material according to claim 1, wherein: The dispersion method in step S6 is a stirring method or an ultrasonic method.

7. The preparation method of an iron oxide-cerium oxide composite material according to claim 1, wherein: In step S6, the molar ratio of Fe3O4 to cerium salt is (1 - 20):1; or, the molar ratio of Fe3O4 to cerium salt is 1:(2 - 20).

8. The preparation method of an iron oxide-cerium oxide composite material according to claim 1, wherein: The volume ratio of ultrapure water to ethanol in step S6 is (1 - 5):

1.

9. An iron oxide-cerium oxide composite material, characterized in that: Prepared by the preparation method of an iron oxide-cerium oxide composite material according to any one of claims 1 - 8.

10. The application of the iron oxide-cerium oxide composite material according to claim 9 as a catalyst in a lithium-sulfur battery.

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