FeTiO3-BiFeO3 heterojunction as well as preparation method and application thereof

Abstract

The invention discloses a FeTiO3-BiFeO3 heterojunction. The FeTiO3-BiFeO3 heterojunction is of a p-n heterojunction structure formed by ferrous titanate and bismuth ferrite according to the mass ratio of 1: (0.5-2). The preparation method comprises the following steps: (1) preparing ferrous titanate powder by utilizing a hydrothermal synthesis method; (2) preparing bismuth ferrite powder by using a hydrothermal synthesis method; (3) adding water into the ferrous titanate powder, carrying out uniform ultrasonic dispersion, then adding the bismuth ferrite powder, carrying out ultrasonic dispersion, and then continuously stirring and mixing to obtain a mixed dispersion liquid; (4) putting the mixed dispersion liquid into a reaction kettle, carrying out hydrothermal reaction, and carrying out solid-liquid separation after the reaction is finished; and washing the solid precipitate obtained by separation, and then drying the solid precipitate to obtain the FeTiO3-BiFeO3 heterojunction. When the material is used for preparing the anode material of the lithium battery, the technical problems of poor lithium storage performance, electrochemical performance, cycling stability and the like of the existing ferrous titanate anode material can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of heterojunction preparation, in particular to a FeTiO3-BiFeO3 heterojunction and its preparation method and application. Background Art

[0002] Transition metal-based compounds have become a research hotspot due to their unique physicochemical structure, synergistic reactions between metal ions, and multiple oxidation states. Among them, transition metal oxides have attracted widespread attention due to their wide availability, ease of synthesis, and exceptionally high storage capacity exceeding theoretical values. Transition metal oxide anodes, MOx (M is a transition metal element such as Fe, Co, Ni), have high capacity and structural stability. However, due to the large volume expansion and the low intrinsic electronic conductivity of the material itself, the electrode material undergoes irreversible structural degradation during the cycle, and the particles agglomerate, which slows down the electrochemical reaction kinetics, ultimately leading to a decrease in battery capacity and poor long-term cycle stability.

[0003] Among numerous anode materials, binary transition metal oxides offer broader application prospects compared to other oxide-based anode materials due to their higher reversible capacity, improved structural stability, and high electronic conductivity. Ferrous titanate (FeTiO3), a novel binary transition metal oxide anode material, possesses high theoretical capacity and cycling stability. Furthermore, FeTiO3 possesses a unique [BO6] octahedral structure, which imparts rich physicochemical properties. As an electrode material, FeTiO3 exhibits both unique intercalation and conversion lithium storage mechanisms during cycling. This "dual-mechanism synergy" results in fast intercalation kinetics and good reversibility. However, FeTiO3's low electronic conductivity and ion mobility restrict its stability during cycling.

[0004] A heterojunction is a structure formed by coupling two or more semiconductor materials with different band gaps. This heterogeneous structure is extremely effective in improving the material's conductivity. The heterojunction structure generates a potential difference at its interface, redistributing charge across the interface and forming a built-in electric field. This built-in electric field significantly reduces the energy barrier for ion and electron transport, improving the material's charge transport capability.

[0005] Patent CN117374262A discloses an endogenous heterojunction anode material and its preparation method. Using graphene oxide as a substrate, the material utilizes the cross-linking properties of a cross-linking agent to sinter in a reducing atmosphere to form an endogenous heterojunction composed of FeTiO3 and Fe2TiO5. This improves the conductivity of the electrode material itself, resulting in an excellent anode material. However, this FeTiO3@Fe2TiO5 endogenous heterojunction and its preparation method still have the following drawbacks: the preparation process is relatively complex, and the heterojunction is directly generated in a reducing atmosphere, resulting in uncontrollable products. Therefore, it is necessary to construct a new ferrous titanate heterojunction to address the technical problems of existing ferrous titanate anode materials, such as poor lithium storage performance, electrochemical performance, and cycle stability. Summary of the Invention

[0006] To this end, the technical problem to be solved by the present invention is to provide a FeTiO3-BiFeO3 heterojunction and its preparation method and application, so as to solve the technical problems of the existing ferrous titanate anode material such as poor lithium storage performance, electrochemical performance and cycle stability.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions: A FeTiO3-BiFeO3 heterojunction is provided, wherein a pn heterojunction structure is formed by mixing ferrous titanate and bismuth ferrite in a mass ratio of 1:(0.5-2).

[0008] A method for preparing a FeTiO3-BiFeO3 heterojunction comprises the following steps: Step (1), using tetrabutyl titanate as a titanium source and a soluble ferrous salt as an iron source, and preparing ferrous titanate by a hydrothermal synthesis method to obtain ferrous titanate powder; Step (2), using a bismuth salt as a bismuth source and a soluble trivalent iron salt as an iron source, preparing bismuth ferrite by a hydrothermal synthesis method to obtain bismuth ferrite powder; Step (3), adding ferrous titanate powder to water and uniformly dispersing it by ultrasonication, then adding bismuth ferrite powder and continuing to disperse it by ultrasonication, and continuing to stir after the ultrasonic dispersion until the two powders are mixed and dispersed uniformly to obtain a mixed dispersion; Step (4): placing the mixed dispersion in a reactor for hydrothermal reaction, and separating the solid and liquid after the reaction is completed; washing and drying the separated solid precipitate to obtain the above-mentioned FeTiO3-BiFeO3 heterojunction.

[0009] Compared with the conventional sol-gel method and solid-phase method, the ferrous titanate and bismuth ferrite synthesized by the hydrothermal synthesis method in the present invention have better crystallinity and better electrical cycling performance as electrode materials alone; the FeTiO3-BiFeO3 heterojunction prepared by the hydrothermal synthesis method of the present invention has significantly improved electrical cycling performance as an electrode material.

[0010] In the above-mentioned method for preparing the FeTiO3-BiFeO3 heterojunction, in step (1), the method for preparing ferrous titanate powder is: Step (1-1), adding tetrabutyl titanate dropwise into tetrabutylammonium hydroxide solution to obtain a mixed solution A; Step (1-2), heating and stirring the mixed solution A until it becomes transparent, then adding the ferrous sulfate solution and continuing to heat and stir, then adding potassium hydroxide while heating and stirring, and stirring to obtain a mixed solution B; Step (1-3): placing the mixed solution B in a reactor for hydrothermal reaction, and separating the solid and liquid after the reaction is completed; washing and drying the separated solid precipitate to obtain ferrous titanate powder.

[0011] The above-mentioned preparation method of the FeTiO3-BiFeO3 heterojunction, in step (1-1), the volume ratio of tetrabutylammonium hydroxide to water in the tetrabutylammonium hydroxide solution is 1:(10-12), and the pH of the tetrabutylammonium hydroxide solution at this concentration is moderate, which is conducive to the subsequent reaction to form ferrous titanate; the ratio of the total volume of tetrabutyl titanate added to the volume of tetrabutylammonium hydroxide is 1:(1.5-2.0); the addition rate of tetrabutyl titanate is 1.0-1.5 mL / min; the addition rate of tetrabutyl titanate into tetrabutylammonium hydroxide and the volume ratio of the total amount of tetrabutyl titanate added to tetrabutylammonium hydroxide are controlled to ensure that the tetrabutyl titanate is fully hydrolyzed in the mixed solution A and avoid the formation of white flocculent precipitation; In step (1-2), the molar ratio of ferrous sulfate to tetrabutyl titanate is (1.5-2.0):1; the molar concentration of the ferrous sulfate solution is 1.0-3.0 mol / L; the molar ratio of potassium hydroxide to ferrous sulfate is (1.5-3.0):1; after adding the ferrous sulfate solution, heating and stirring are continued for 20-30 minutes, and after adding the potassium hydroxide, heating and stirring are continued for 10-15 minutes; throughout the process of step (1-2), the heating and stirring temperature is 60-70°C, and the heating and stirring rate is 400-500 rpm; by controlling the concentration and amount of the ferrous sulfate solution, the amount of potassium hydroxide, etc., the ratio of the titanium source and the iron source in the mixed solution B is adjusted to an appropriate range, and the heating and stirring temperature and heating and stirring rate throughout the process of step (1-2) are controlled, which can effectively avoid the oxidation and decomposition of the effective ingredients in the system, reduce the generation of impurities such as ferrosoferric oxide during the preparation of ferrous titanate, and thus ensure the purity of the target product; In step (1-3), the hydrothermal reaction temperature is 210-230°C, and the hydrothermal reaction time is 10-16h; if the hydrothermal reaction temperature is lower than 210°C, the iron source will generate a ferroferric oxide impurity phase, and if the hydrothermal reaction temperature is higher than 230°C, a titanium dioxide impurity phase will be generated; the present invention controls the hydrothermal reaction temperature and controls the hydrothermal reaction time within the range of 10-16h, so that the titanium source and the iron source in the reaction system can fully react to generate ferrous titanate, reduce the generation of impurities such as ferroferric oxide and titanium dioxide, ensure the purity of the target product, and provide a basis for the subsequent preparation of FeTiO3-BiFeO3 heterojunction; during washing, deionized water and anhydrous ethanol are used for repeated washing for 3-5 times; the drying conditions are: drying at a temperature of 70-80°C for 10-16h; under these drying conditions, both moisture can be fully removed and the oxidation of ferrous titanate can be effectively avoided.

[0012] The preparation method of the above-mentioned FeTiO3-BiFeO3 heterojunction and the preparation method of bismuth ferrite powder are as follows: Step (2-1), adding bismuth salt and soluble trivalent iron salt to an inorganic acid solution and stirring to dissolve, to obtain a mixed solution C; Step (2-2), adding potassium hydroxide solution A dropwise to mixed solution C until the precipitation reaction is complete to obtain a mixed reaction system; ultrasonically treating the mixed reaction system and stirring to mix, and then performing solid-liquid separation; washing the separated solid precipitate with deionized water until neutral to obtain a solid intermediate product, the main components of which are iron hydroxide and bismuth hydroxide; Step (2-3), redispersing the solid intermediate product in potassium hydroxide solution B, ultrasonically treating the solution, and stirring to obtain a mixed solution D; Step (2-4): placing the mixed solution D in a reactor for hydrothermal reaction, and separating the solid and liquid after the reaction is completed; washing and drying the separated solid precipitate to obtain bismuth ferrite powder.

[0013] In the preparation method of the above-mentioned FeTiO3-BiFeO3 heterojunction, in step (2-1), the soluble bismuth salt is bismuth nitrate pentahydrate or anhydrous bismuth nitrate, and the soluble trivalent iron salt is ferric nitrate nonahydrate or anhydrous ferric nitrate; the inorganic acid solution is a dilute nitric acid solution with a volume fraction of 5 to 10%; in the mixed solution C, the molar ratio of the soluble bismuth salt to the soluble trivalent iron salt is (1.0 to 1.5):1 (when the molar ratio of the two salts is within this range, the formation of other impurities other than bismuth ferrite can be effectively reduced), and the molar concentration of the soluble trivalent iron salt is 0.2 to 0.4 mol / L; by controlling the volume fraction of the dilute nitric acid solution and the molar concentrations of the iron salt and the bismuth salt in the mixed solution C, the bismuth salt and the iron salt can be fully dissolved and completely dissociated in the mixed solution C, which is conducive to the subsequent full reaction to synthesize bismuth ferrite; In step (2-2), the molar concentration of potassium hydroxide solution A is 1 to 4 mol / L; the amount of potassium hydroxide solution A added is controlled so that the pH of the mixed reaction system is 10 to 12; the ultrasonic treatment time is 10 to 15 minutes, the stirring time is 20 to 30 minutes, and the stirring rate is 400 to 500 rpm; by controlling the pH of the mixed reaction system within a specific range, the intermediate reaction can be fully carried out; In step (2-3), the molar concentration of potassium hydroxide solution B is 5 to 10 mol / L; in the mixed solution D, the molar ratio of iron to potassium hydroxide is 1:(60 to 90); the ultrasonic treatment time is 10 to 15 minutes, the stirring time is 20 to 30 minutes, and the stirring rate is 400 to 500 rpm; In step (2-4), the hydrothermal reaction temperature is 230-250° C., and the hydrothermal reaction time is 10-16 hours. If the hydrothermal reaction temperature is lower than 230° C., a Bi2Fe4O9 impurity phase will be formed. If the hydrothermal reaction temperature is higher than 250° C., or the hydrothermal reaction time exceeds the above range, the purity of the final bismuth ferrite powder will also decrease. During washing, deionized water and anhydrous ethanol are used for repeated washing 3-5 times. The drying conditions are: drying at 70-80° C. for 10-16 hours. This drying condition can completely dry the bismuth ferrite powder without causing decomposition of the bismuth ferrite.

[0014] In the above-mentioned preparation method of the FeTiO3-BiFeO3 heterojunction, in step (3), the particle size range of the ferrous titanate powder is 0.05-0.10 μm, and the particle size range of the bismuth ferrite powder is 0.05-0.10 μm; the time for the two ultrasonic dispersions is 10-15 minutes; after the second ultrasonic dispersion, stirring is continued for 20-30 minutes, and the stirring rate is 400-500 rpm; in the mixed dispersion, the mass ratio of ferrous titanate to bismuth ferrite is 1:(0.5-2), and the mass concentration of ferrous titanate is 0.03-0.05 mol / L.

[0015] In the above-mentioned preparation method of the FeTiO3-BiFeO3 heterojunction, in step (4), the hydrothermal reaction temperature is 150-180°C, and the hydrothermal reaction time is 10-16 hours. Under the reaction conditions, ferrous titanate of a specific particle size and bismuth ferrite of a specific particle size can fully react to form a FeTiO3-BiFeO3 heterojunction. If the temperature is too low, it will affect the formation of the heterojunction structure. If the temperature is too high, it will cause the ferrous titanate and bismuth ferrite to decompose. During washing, deionized water and anhydrous ethanol are used for repeated washing for 3-5 times. The drying conditions are: drying at a temperature of 70-80°C for 10-16 hours.

[0016] In the above-mentioned method for preparing the FeTiO3-BiFeO3 heterojunction, in step (1), the method for preparing ferrous titanate powder is: Step (1-1), tetrabutyl titanate is added dropwise to a tetrabutylammonium hydroxide solution to obtain a mixed solution A; in the tetrabutylammonium hydroxide solution, the volume ratio of tetrabutylammonium hydroxide to water is 1:11.5; the volume ratio of the total volume of the added tetrabutyl titanate to the volume of the tetrabutylammonium hydroxide is 1:1.8; the addition rate of the tetrabutyl titanate is 1.0 mL / min; Step (1-2): After heating and stirring the mixed solution A at 60° C. until it becomes transparent, a 1.5 mol / L ferrous sulfate solution is added, and heating and stirring are continued for 30 minutes. Potassium hydroxide is then added and heated and stirred for 10 minutes to obtain a mixed solution B; the molar ratio of ferrous sulfate to tetrabutyl titanate is 1.875:1, and the molar ratio of potassium hydroxide to ferrous sulfate is 2.4:1; the stirring rate in this step is 450 rpm; Step (1-3): placing the mixed solution B in a reactor and hydrothermally reacting it at 220°C for 12 hours, and separating the solid and liquid after the reaction is completed; washing the separated solid precipitate repeatedly with deionized water and anhydrous ethanol for 3 times, and drying it at 80°C for 12 hours to obtain ferrous titanate powder; The preparation method of bismuth ferrite powder is as follows: Step (2-1), adding bismuth nitrate pentahydrate and ferric nitrate nonahydrate in a molar ratio of 1.2:1 to a 10% volume fraction dilute nitric acid solution, stirring and dissolving to obtain a mixed solution C; the molar concentration of ferric nitrate nonahydrate in the mixed solution C is 0.25 mol / L; Step (2-2), adding a potassium hydroxide solution A having a molar concentration of 2 mol / L to the mixed solution C until the precipitation reaction is complete to obtain a mixed reaction system, and controlling the amount of potassium hydroxide solution A added so that the pH of the mixed reaction system is 11; ultrasonically treating the mixed reaction system for 10 minutes and stirring for 30 minutes at a stirring rate of 450 rpm, followed by solid-liquid separation; washing the separated solid precipitate with deionized water until neutral to obtain a solid intermediate product; In step (2-3), the solid intermediate product was redispersed in a potassium hydroxide solution B having a molar concentration of 8 mol / L, ultrasonically treated for 10 minutes, and stirred for 30 minutes at a stirring rate of 450 rpm to obtain a mixed solution D; in the mixed solution D, the molar ratio of iron element to potassium hydroxide was 1:80; Step (2-4), placing the mixed solution D in a reactor and hydrothermally reacting it at 240°C for 12 hours, and separating the solid and liquid after the reaction is completed; washing the separated solid precipitate repeatedly with deionized water and anhydrous ethanol three times, and drying it at 80°C for 12 hours to obtain bismuth ferrite powder; In step (3), the particle size range of ferrous titanate powder is 0.05 to 0.10 μm, and the particle size range of bismuth ferrite powder is 0.05 to 0.10 μm; the time for both ultrasonic dispersions is 10 min; stirring is continued for 30 min after the second ultrasonic dispersion, and the stirring rate is 450 rpm; in the mixed dispersion, the mass ratio of ferrous titanate to bismuth ferrite is 1:(0.5 to 2), and the mass concentration of ferrous titanate is 0.033 mol / L; In step (4), the hydrothermal reaction temperature is 160°C, and the hydrothermal reaction time is 12 hours. During washing, deionized water and anhydrous ethanol are used for repeated washing three times. The drying condition is: drying at 80°C for 12 hours.

[0017] An application of a FeTiO3-BiFeO3 heterojunction is to use the above-mentioned FeTiO3-BiFeO3 heterojunction to prepare anode materials for lithium batteries.

[0018] The technical solution of the present invention achieves the following beneficial technical effects: 1. The preparation method of the FeTiO3-BiFeO3 heterojunction of the present invention successfully constructs the FeTiO3-BiFeO3 heterojunction structure by a step-by-step hydrothermal method. The method is simple to operate, has a fast synthesis speed, and stable synthetic components. The prepared FeTiO3-BiFeO3p-n heterojunction can be used as a lithium battery anode material. The FeTiO3-BiFeO3 heterojunction structure prepared by the FeTiO3-BiFeO3 heterojunction preparation method of the present invention can form a heterogeneous interface between FeTiO3 and BiFeO3, thereby generating a certain potential difference at the heterogeneous interface, thereby forming a built-in electric field at the interface; the present invention selects a hydrothermal synthesis method to prepare FeTiO3 and BiFeO3 respectively, and by controlling the hydrothermal synthesis process parameters, the crystallinity of the prepared FeTiO3 and BiFeO3 can be significantly improved. The two are then hydrothermally synthesized by controlling the ratio of the two and the hydrothermal synthesis process parameters, so that the built-in electric field formed by the prepared FeTiO3-BiFeO3 heterojunction has a high electronic state density and a low ion diffusion barrier, greatly improving its ion transport efficiency. At the same time, the unique heterojunction structure of the FeTiO3-BiFeO3 prepared by the present invention can also effectively improve the lithium storage capacity of the material itself, effectively curb the decomposition of effective substances in FeTiO3 during the cycle process, and greatly improve the stability of the electrode material.

[0019] 2. In the FeTiO3-BiFeO3 heterojunction prepared by the present invention, BiFeO3 is an Fe-based binary transition metal oxide similar to FeTiO3, and its structure is also a stable perovskite structure, and both are rhombohedral crystal systems. At the same time, FeTiO3 and BiFeO3 are n-type and p-type semiconductors, respectively, which realize the movement of electrons through electron / hole transitions, and a corresponding pn heterostructure is formed at the interface between the two, thereby promoting charge transfer and improving lithium ion adsorption. Therefore, this unique heterojunction structure can effectively improve the lithium storage performance and electrochemical properties of the material itself. In addition, the built-in electric field of the FeTiO3-BiFeO3 heterojunction can redistribute the charge, thereby effectively reducing the diffusion resistance of ions and charges, increasing the carrier concentration, and thus significantly improving the cycle performance of the battery.

[0020] 3. The present invention uses tetrabutyl titanate as a titanium source and ferrous sulfate as an iron source to prepare ferrous titanate by a hydrothermal synthesis method. By controlling the molar ratio of ferrous sulfate to tetrabutyl titanate, the amount of potassium hydroxide, the hydrothermal synthesis reaction temperature, the reaction time, and the stirring rate of the entire preparation process, the prepared ferrous titanate can have an ideal crystallinity. Compared with conventional sol-gel and solid-phase methods, it has better electrical cycling performance as an electrode material. The present invention uses bismuth nitrate pentahydrate as a bismuth source and ferric nitrate nonahydrate as an iron source to prepare bismuth ferrite by a hydrothermal synthesis method. By controlling the ratio of each raw material and reaction parameters in the preparation process, the crystallinity of the obtained bismuth ferrite can be significantly optimized, thereby improving its electrical cycling performance as an electrode material. The ferrous titanate and bismuth ferrite prepared by the hydrothermal synthesis method of the present invention are subjected to the hydrothermal synthesis reaction of the present invention. By controlling the ratio of the two and the hydrothermal synthesis reaction conditions, the ferrous titanate and bismuth ferrite can form a stable FeTiO3-BiFeO3p-n heterojunction structure. When used as an electrode material, the lithium storage performance and electrochemical performance are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD comparison diagram of different anode materials in the embodiments of the present invention; Figure 2 TEM morphology of the FeTiO3-1BiFeO3 heterojunction prepared in an embodiment of the present invention; Figure 3 HRTEM morphology of the FeTiO3-1BiFeO3 heterojunction prepared in an embodiment of the present invention; Figure 4 Cycling capacity diagram of batteries assembled with different anode materials in the embodiment of the present invention (current size is 0.1 Ag -1 ); Figure 5Constant current charge and discharge curve of the battery assembled with the prepared FeTiO3-2BiFeO3 heterojunction as the anode material in the embodiment of the present invention (current size is 0.1 A g -1 ); Figure 6 Constant current charge and discharge curve of the battery assembled with the prepared FeTiO3-1BiFeO3 heterojunction as the anode material in the embodiment of the present invention (current size is 0.1 A g -1 ); Figure 7 Constant current charge and discharge curve of the battery assembled with the prepared FeTiO3-0.5BiFeO3 heterojunction as the anode material in the embodiment of the present invention (current size is 0.1 A g -1 ); Figure 8 Cycling capacity diagram of batteries assembled with different anode materials in the embodiment of the present invention (current size is 1.0 Ag -1 ); Figure 9 The charge and discharge curves of batteries assembled with different anode materials in the embodiment of the present invention (current size is 0.1~2.0 A g -1 ); Figure 10 CV curves at different scan rates (scan rate range of 0.1 mV to 2 mV) for a battery assembled with the prepared FeTiO3-1BiFeO3 heterojunction as the anode material in an embodiment of the present invention; Figure 11 Fitting curves of the peak current of the CV curve and the square root of the scan rate at different scan rates for batteries assembled with the prepared FeTiO3 and FeTiO3-1BiFeO3 heterojunction as anode materials in the embodiment of the present invention; Figure 12 Fitting curve of the logarithm of the peak current of the CV curve and the logarithm of the scan rate at different scan rates for a battery assembled with the prepared FeTiO3-1BiFeO3 heterojunction as the anode material in an embodiment of the present invention; Figure 13 Pseudocapacitance contribution diagram of a battery assembled with the prepared FeTiO3-1BiFeO3 heterojunction as the anode material at different scan rates in an embodiment of the present invention; Figure 14 The Quisted impedance diagram of a battery assembled with the prepared FeTiO3-1BiFeO3 heterojunction as the anode material in an embodiment of the present invention; Figure 15 Cycling capacity diagram of batteries assembled with BiFeO3 samples prepared in the embodiment of the present invention and BiFeO3 samples prepared by conventional sol-gel method and solid phase method as anode materials (current size is 1.0 A g -1 ); Figure 16 TEM morphology of the FeTiO3-2BiFeO3 heterojunction prepared in an embodiment of the present invention; Figure 17 HRTEM morphology of the FeTiO3-2BiFeO3 heterojunction prepared in an embodiment of the present invention; Figure 18 TEM morphology of the FeTiO3-0.5BiFeO3 heterojunction prepared in an embodiment of the present invention; Figure 19 HRTEM morphology of the FeTiO3-0.5BiFeO3 heterojunction prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The method for preparing the FeTiO3-BiFeO3 heterojunction in this embodiment includes the following steps: 1. Preparation of FeTiO3 powder Measure 5.2 mL of tetrabutylammonium hydroxide and add it to a beaker containing 60 mL of deionized water. Stir for 10 minutes. Measure 2.818 mL of tetrabutyl titanate and slowly add it dropwise (at a rate of 1.0 mL / min) to the mixture. Transfer the mixture to a water bath and heat and stir at 60°C (450 rpm) until the solution becomes transparent. Then, dissolve 2.224 g of FeSO₄ in 10 mL of deionized water to obtain a ferrous sulfate solution. Add the ferrous sulfate solution to the transparent solution and continue heating and stirring at 450 rpm for 30 minutes. Then, add 2 g of KOH powder and continue heating and stirring at 450 rpm for 10 minutes. Transfer the resulting mixture to a 100 mL reactor and incubate at 220°C for 12 hours. After the reaction is completed, the solid and liquid are separated, and the obtained solid precipitate is repeatedly washed with deionized water and ethanol three times, and dried in an oven at 80°C for 12 h to obtain FeTiO3 powder. The powder is ground to a particle size of 0.05-0.10 μm and set aside.

[0023] 2. Preparation of BiFeO3 powder Weigh 2.4499 g of Bi(NO₃)₃·5H₂O and 2.0404 g of Fe(NO₃)₃·9H₂O into a beaker containing 20 mL of dilute nitric acid (10% by volume) and stir until the crystals are completely dissolved. Prepare an excess of 2 M KOH solution and slowly add it dropwise to the mixture. A large amount of orange-yellow precipitate will form, gradually darkening in color. Continue adding KOH solution dropwise to adjust the pH to 11, allowing the mixture to completely precipitate. Ultrasonicate the reaction mixture for 10 minutes, then stir rapidly at 450 rpm for 30 minutes to evenly disperse the precipitate. Wash repeatedly with deionized water and centrifuge until the precipitate becomes neutral. Then, add 50 mL of 8 M KOH solution to the precipitate, sonicate for 10 minutes, and stir rapidly at 450 rpm for 30 minutes. Transfer the resulting solution to a 100 mL reactor and incubate at 240°C for 12 hours. The obtained precipitate was repeatedly washed with deionized water and ethanol three times, and dried in an oven at 80°C for 12 h to obtain BiFeO3 powder. The BiFeO3 powder was ground to a particle size of 0.05-0.10 μm and set aside.

[0024] 3. Preparation of FeTiO3-BiFeO3 Weigh FeTiO3 powder and BiFeO3 powder in mass ratios of 2:1, 1:1, and 1:2, respectively. Add FeTiO3 powder to 60 mL of deionized water and sonicate for 10 minutes. Then, add BiFeO3 powder to the dispersion and sonicate for 10 minutes. Stir rapidly at 450 rpm for 30 minutes to uniformly disperse the powders. Place the resulting mixed dispersion in a 100 mL reactor and incubate at 160°C for 12 hours. After the reaction, separate the solid and liquid. Wash the resulting solid precipitate three times with deionized water and ethanol, then dry it in an oven at 80°C for 12 hours to obtain FeTiO3-BiFeO3 powder. Grind the powder through a 450-mesh sieve for later use. The FeTiO3-BiFeO3 powders prepared by FeTiO3 powder and BiFeO3 powder with mass ratios of 2:1, 1:1 and 1:2 were named FeTiO3-0.5BiFeO3, FeTiO3-1BiFeO3 and FeTiO3-2BiFeO3 respectively.

[0025] The prepared FeTiO3-0.5BiFeO3, FeTiO3-1BiFeO3 and FeTiO3-2BiFeO3 were used to prepare lithium battery anodes and assembled batteries, and the performance of each electrode material was tested.

[0026] Battery assembly method: First, the electrode materials and acetylene black were thoroughly ground and mixed in a mortar. Sodium alginate (SA) was then added and further ground and mixed in a ratio of 8:1:1. Deionized water was added dropwise to prepare a slurry, which was then coated onto a copper foil specifically designed for the anode. The slurry was dried in a vacuum oven at 80°C for 12 hours and then cut. The electrolyte consisted of 1 mol / L LiPF6 and EC:DMC:DEC (1:1:1 by volume). A polypropylene (PP) microporous membrane served as the separator, and lithium metal sheets served as the electrodes. Finally, 2032-sized button cell batteries were assembled in an argon-protected glove box.

[0027] Performance test method: Connect the assembled electrode sheet to the blue electric test system, set the voltage window to 0.01~3V, and select the current density to 0.1 A g -1 , test the cross-current charge and discharge cycle. Continue to set the current density to 0.1 A g-1~2 A g -1 , test rate charge and discharge cycle.

[0028] from Figure 1 It can be seen from the comparison with the PDF card (PDF#22-0169) that the diffraction peaks corresponding to the (110), (211), (210), (220), and (321) crystal planes of FeTiO3 are observed at 2θ of 23.87°, 32.53°, 40.52°, 48.91°, and 53.24°, and the characteristic peaks observed at 2θ of 22.49°, 31.80°, and 32.13° correspond to the (101), (012), and (110) crystal planes of BiFeO3 (PDF#99-0036). Therefore, the diffraction peaks confirm the existence of two phases.

[0029] from Figure 2 It can be seen that the FeTiO3-1BiFeO3 sample presents a relatively obvious hexagonal structure, and there is some overlap at the interface.

[0030] from Figure 3 As can be seen, the HRTEM image clearly presents the heterojunction interface of FeTiO3-1BiFeO3. The blue area with an interplanar spacing of 1.30 Å corresponds to the (101) crystal plane of BiFeO3, while the orange area with an interplanar spacing of 2.55 Å corresponds to the (-110) crystal plane of FeTiO3, indicating the successful synthesis of the heterojunction structure.

[0031] The micromorphological characteristics of the two heterojunctions, FeTiO3-0.5BiFeO3 and FeTiO3-2BiFeO3, are similar to those of the FeTiO3-1BiFeO3 heterojunction. Figures 16 to 19As shown in the figure, it can be seen that the FeTiO3-0.5BiFeO3 and FeTiO3-2BiFeO3 samples synthesized in this embodiment also have heterojunction structures.

[0032] from Figure 4 It can be seen that FeTiO3-1BiFeO3 shows a maximum of 984.1mAhg after 250 cycles. -1 The high capacity performance of FeTiO3 was significantly reduced to 631.5 mAh g -1 , the BiFeO3 capacity decayed to 484 mAh g -1 .

[0033] from Figures 5 to 7 It can be seen that the charge and discharge platform of the constant current charge and discharge curve of FeTiO3-BiFeO3 with different ratios changes significantly as the cycle proceeds.

[0034] from Figure 8 It can be seen that at 1 A g -1 At the same current density, the capacity of FeTiO3-1BiFeO3 after 1000 cycles is 268.7 mAh g -1 Still better than FeTiO3 (59mAh g -1 ) and BiFeO3 (26 mAh g -1 ), and has good cycle stability.

[0035] from Figure 9 It can be seen that as the current density increases from 100, 200, 500, 1000 to 2000 mA g -1 , the discharge of FeTiO3-BiFeO3 is more stable; this indicates that FeTiO3-1BiFeO3 exhibits excellent rate performance.

[0036] In summary, compared with the two heterojunctions of FeTiO3-0.5BiFeO3 and FeTiO3-2BiFeO3, the anode material prepared with FeTiO3-1BiFeO3 heterojunction exhibits better electrochemical performance, and the performance of the battery assembled using it was further tested.

[0037] from Figures 10 to 13 It can be seen that the CV curves at various scan rates exhibit similar trends, with no obvious polarization phenomenon. During the cycling process, the electrode material exhibits both battery properties and pseudocapacitive properties. This indicates that the construction of the heterojunction increases the lithium ion diffusion coefficient of the sample, promotes the lithium ion transmission efficiency, and thus improves the battery's cycling performance; as the scan rate increases, the pseudocapacitive contribution also increases.

[0038] from Figure 14It can be seen that through the construction of the heterojunction structure, the electrolyte resistance of the FeTiO3-1BiFeO3 sample is significantly better than that of the FeTiO3 sample ( R e ) and charge transfer resistance ( R ct ) is significantly reduced, and the diffusion resistance (W0-R) is significantly reduced, which corresponds to the increase in the ion diffusion coefficient.

[0039] Figure 15 The figure shows the electrical cycling performance of BiFeO3 samples prepared by different methods as electrode materials. It can be seen from the figure that compared with the conventional sol-gel method and solid-phase method, the BiFeO3 sample synthesized by the hydrothermal method in this embodiment shows better electrical cycling performance as an electrode material.

[0040] In summary, the present invention first prepared the FeTiO3-BiFeO3 heterojunction structure anode material in a hydrothermal manner. The material has lower internal resistance and higher ion diffusion coefficient, and its excellent electrochemical performance is attributed to its unique heterojunction structure. The built-in electric field formed by the construction of the heterojunction structure causes the electrons inside the material to be redistributed, greatly reducing the diffusion resistance of ions and charges, thereby significantly improving the electrical properties of the material itself. At the same time, due to the formation of the interface, the structure of the material itself is more stable, and it is not easy to collapse the structure at high current density, which greatly improves the cycle performance of the material. Compared with the FeTiO3 and BiFeO3 anode materials reported previously, at a current density of 0.1A g -1 After 250 cycles, the capacity decay of the FeTiO3-BiFeO3 sample was significantly alleviated to 984.1 mAh g -1 Under high current and long cycle conditions (1A g -1 The capacity of the FeTiO3-BiFeO3 sample is 268.7 mAh g -1 .

[0041] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A FeTiO3-BiFeO3 heterojunction, characterized in that A pn heterojunction structure is formed by ferrous titanate and bismuth ferrite in a mass ratio of 1:(0.5-2).

2. A method for preparing a FeTiO3-BiFeO3 heterojunction, characterized in that: The steps include: Step (1), using tetrabutyl titanate as a titanium source and a soluble ferrous salt as an iron source, and preparing ferrous titanate by a hydrothermal synthesis method to obtain ferrous titanate powder; Step (2), using a bismuth salt as a bismuth source and a soluble trivalent iron salt as an iron source, preparing bismuth ferrite by a hydrothermal synthesis method to obtain bismuth ferrite powder; Step (3), adding ferrous titanate powder to water and uniformly dispersing it by ultrasonication, then adding bismuth ferrite powder and continuing to disperse it by ultrasonication, and continuing to stir after the ultrasonic dispersion until the two powders are mixed and dispersed uniformly to obtain a mixed dispersion; Step (4), placing the mixed dispersion in a reactor for hydrothermal reaction, and separating the solid and liquid after the reaction is completed; The separated solid precipitate is washed and then dried to obtain the FeTiO3-BiFeO3 heterojunction as claimed in claim 1.

3. The method for preparing a FeTiO3-BiFeO3 heterojunction according to claim 2, characterized in that: In step (1), the preparation method of ferrous titanate powder is: Step (1-1), adding tetrabutyl titanate dropwise into tetrabutylammonium hydroxide solution to obtain a mixed solution A; Step (1-2), heating and stirring the mixed solution A until it becomes transparent, then adding the ferrous sulfate solution and continuing to heat and stir, then adding potassium hydroxide while heating and stirring, and stirring to obtain a mixed solution B; Step (1-3): placing the mixed solution B in a reactor for hydrothermal reaction, and separating the solid and liquid after the reaction is completed; washing and drying the separated solid precipitate to obtain ferrous titanate powder.

4. The method for preparing a FeTiO3-BiFeO3 heterojunction according to claim 3, characterized in that: In step (1-1), in the tetrabutylammonium hydroxide solution, the volume ratio of tetrabutylammonium hydroxide to water is 1:(10-12); the ratio of the total volume of tetrabutyl titanate added dropwise to the volume of tetrabutylammonium hydroxide is 1:(1.5-2.0); and the addition rate of tetrabutyl titanate is 1.0-1.5 mL / min; In step (1-2), the molar ratio of ferrous sulfate to tetrabutyl titanate is (1.5-2.0):1; the molar concentration of the ferrous sulfate solution is 1.0-3.0 mol / L; the molar ratio of potassium hydroxide to ferrous sulfate is (1.5-3.0):1; after adding the ferrous sulfate solution, heating and stirring are continued for 20-30 minutes, and after adding the potassium hydroxide, heating and stirring are continued for 10-15 minutes; throughout the entire process of step (1-2), the heating and stirring temperature is 60-70°C, and the heating and stirring rate is 400-500 rpm; In steps (1-3), the hydrothermal reaction temperature is 210-230° C., and the hydrothermal reaction time is 10-16 h. During washing, deionized water and anhydrous ethanol are used for repeated washing 3-5 times. The drying conditions are: drying at 70-80° C. for 10-16 h.

5. The method for preparing a FeTiO3-BiFeO3 heterojunction according to claim 2, characterized in that: The preparation method of bismuth ferrite powder is as follows: Step (2-1), adding bismuth salt and soluble trivalent iron salt to an inorganic acid solution and stirring to dissolve, to obtain a mixed solution C; Step (2-2), adding potassium hydroxide solution A dropwise to mixed solution C until the precipitation reaction is complete to obtain a mixed reaction system; ultrasonically treating the mixed reaction system and stirring to mix, and then performing solid-liquid separation; washing the separated solid precipitate with deionized water until neutral to obtain a solid intermediate product; Step (2-3), redispersing the solid intermediate product in potassium hydroxide solution B, ultrasonically treating the solution, and stirring to obtain a mixed solution D; Step (2-4): placing the mixed solution D in a reactor for hydrothermal reaction, and separating the solid and liquid after the reaction is completed; washing and drying the separated solid precipitate to obtain bismuth ferrite powder.

6. The method for preparing a FeTiO3-BiFeO3 heterojunction according to claim 5, characterized in that: In step (2-1), the soluble bismuth salt is bismuth nitrate pentahydrate or anhydrous bismuth nitrate, and the soluble trivalent iron salt is ferric nitrate nonahydrate or anhydrous ferric nitrate; the inorganic acid solution is a dilute nitric acid solution with a volume fraction of 5 to 10%; in the mixed solution C, the molar ratio of the soluble bismuth salt to the soluble trivalent iron salt is (1.0 to 1.5):1, and the molar concentration of the soluble trivalent iron salt is 0.2 to 0.4 mol / L; In step (2-2), the molar concentration of potassium hydroxide solution A is 1 to 4 mol / L; the amount of potassium hydroxide solution A added is controlled so that the pH of the mixed reaction system is 10 to 12; the ultrasonic treatment time is 10 to 15 minutes, the stirring time is 20 to 30 minutes, and the stirring rate is 400 to 500 rpm; In step (2-3), the molar concentration of potassium hydroxide solution B is 5 to 10 mol / L; in the mixed solution D, the molar ratio of iron to potassium hydroxide is 1:(60 to 90); the ultrasonic treatment time is 10 to 15 minutes, the stirring time is 20 to 30 minutes, and the stirring rate is 400 to 500 rpm; In step (2-4), the hydrothermal reaction temperature is 230-250° C., and the hydrothermal reaction time is 10-16 h. During washing, deionized water and anhydrous ethanol are used for repeated washing 3-5 times. The drying condition is: drying at 70-80° C. for 10-16 h.

7. The method for preparing a FeTiO3-BiFeO3 heterojunction according to claim 2, characterized in that: In step (3), the particle size range of ferrous titanate powder is 0.05 to 0.10 μm, and the particle size range of bismuth ferrite powder is 0.05 to 0.10 μm; the time for both ultrasonic dispersions is 10 to 15 minutes; stirring is continued for 20 to 30 minutes after the second ultrasonic dispersion, and the stirring rate is 400 to 500 rpm; in the mixed dispersion, the mass ratio of ferrous titanate to bismuth ferrite is 1:(0.5 to 2), and the mass concentration of ferrous titanate is 0.03 to 0.05 mol / L.

8. The method for preparing a FeTiO3-BiFeO3 heterojunction according to claim 2, characterized in that: In step (4), the hydrothermal reaction temperature is 150-180°C, and the hydrothermal reaction time is 10-16 hours. During washing, deionized water and anhydrous ethanol are used for repeated washing 3-5 times. The drying conditions are: drying at 70-80°C for 10-16 hours.

9. The method for preparing a FeTiO3-BiFeO3 heterojunction according to claim 2, characterized in that: In step (1), the preparation method of ferrous titanate powder is: Step (1-1), adding tetrabutyl titanate dropwise to a tetrabutylammonium hydroxide solution to obtain a mixed solution A; in the tetrabutylammonium hydroxide solution, the volume ratio of tetrabutylammonium hydroxide to water is 1:11.5; the ratio of the total volume of the added tetrabutyl titanate to the volume of the tetrabutylammonium hydroxide is 1:1.8; the dropping rate of the tetrabutyl titanate is 1 mL / min; In step (1-2), after heating and stirring the mixed solution A at 60° C. until it becomes transparent, a 1.5 mol / L ferrous sulfate solution is added and the mixture is stirred for 30 minutes, followed by the addition of potassium hydroxide and stirring for 10 minutes to obtain a mixed solution B; the volume ratio of the ferrous sulfate solution to the mixed solution A is 1:6.8, and the molar ratio of potassium hydroxide to ferrous sulfate is 2.4:1; the stirring rate in this step is 450 rpm; Step (1-3): placing the mixed solution B in a reactor and hydrothermally reacting it at 220°C for 12 hours, and separating the solid and liquid after the reaction is completed; washing the separated solid precipitate repeatedly with deionized water and anhydrous ethanol for 3 times, and drying it at 80°C for 12 hours to obtain ferrous titanate powder; The preparation method of bismuth ferrite powder is as follows: Step (2-1), adding bismuth nitrate pentahydrate and ferric nitrate nonahydrate in a molar ratio of 1.2:1 to a 10% volume fraction dilute nitric acid solution, stirring and dissolving to obtain a mixed solution C; the molar concentration of trivalent iron ions is 0.25 mol / L; Step (2-2), adding a potassium hydroxide solution A having a molar concentration of 2 mol / L to the mixed solution C until the precipitation reaction is complete to obtain a mixed reaction system, and controlling the amount of potassium hydroxide solution A added so that the pH of the mixed reaction system is 11; ultrasonically treating the mixed reaction system for 10 minutes and stirring for 30 minutes at a stirring rate of 450 rpm, followed by solid-liquid separation; washing the separated solid precipitate with deionized water until neutral to obtain a solid intermediate product; In step (2-3), the solid intermediate product was redispersed in a potassium hydroxide solution B having a molar concentration of 8 mol / L, ultrasonically treated for 10 minutes, and stirred for 30 minutes at a stirring rate of 450 rpm to obtain a mixed solution D; in the mixed solution D, the molar ratio of iron element to potassium hydroxide was 1:80; Step (2-4), placing the mixed solution D in a reactor and hydrothermally reacting it at 240°C for 12 hours, and separating the solid and liquid after the reaction is completed; washing the separated solid precipitate repeatedly with deionized water and anhydrous ethanol three times, and drying it at 80°C for 12 hours to obtain bismuth ferrite powder; In step (3), the particle size range of the ferrous titanate powder is 0.1 to 0.3 μm, and the particle size range of the bismuth ferrite powder is 0.1 to 0.3 μm; the time for both ultrasonic dispersions is 10 min; stirring is continued for 30 min after the second ultrasonic dispersion, and the stirring rate is 450 rpm; in the mixed dispersion, the mass ratio of ferrous titanate to bismuth ferrite is 1:(0.5 to 2), and the mass concentration of ferrous titanate is 0.033 mol / L; In step (4), the hydrothermal reaction temperature is 160°C, and the hydrothermal reaction time is 12 hours. During washing, deionized water and anhydrous ethanol are used for repeated washing three times. The drying condition is: drying at 80°C for 12 hours.

10. An application of a FeTiO3-BiFeO3 heterojunction, characterized in that: The FeTiO3-BiFeO3 heterojunction prepared by the preparation method of the FeTiO3-BiFeO3 heterojunction according to any one of claims 2 to 9 is used to prepare the anode material of the lithium battery.

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