A FeTiO3-BiFeO3 heterojunction, its preparation method and application

Abstract

This invention discloses a FeTiO3-BiFeO3 heterojunction, which is formed by ferrous titanate and bismuth ferrite in a mass ratio of 1:(0.5-2) to form a p-n heterojunction structure. The preparation method is as follows: Step (1) Ferrous titanate powder is prepared by hydrothermal synthesis; Step (2) Bismuth ferrite powder is prepared by hydrothermal synthesis; Step (3) Ferrous titanate powder is ultrasonically dispersed with water, then bismuth ferrite powder is added and ultrasonically dispersed, followed by further stirring to obtain a mixed dispersion; Step (4) The mixed dispersion is placed in a reaction vessel for hydrothermal reaction, and solid-liquid separation is performed after the reaction; the separated solid precipitate is washed and dried to obtain the FeTiO3-BiFeO3 heterojunction. Using this heterojunction to prepare anode materials for lithium batteries can effectively solve the technical problems of poor lithium storage performance, electrochemical performance, and cycle stability of existing ferrous titanate anode materials.

Description

Technical Field

[0001] This invention relates to the field of heterojunction preparation technology. Specifically, it relates to a FeTiO3-BiFeO3 heterojunction, its preparation method, and its applications. Background Technology

[0002] Transition metal-based compounds have become a research hotspot due to their unique physicochemical structures, 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, specifically MOx (where M represents transition metal elements such as Fe, Co, and Ni), possess high capacity and structural stability. However, due to large volume expansion and low intrinsic electronic conductivity, irreversible structural degradation and particle agglomeration occur during cycling, slowing down electrochemical reaction kinetics and ultimately leading to capacity decay and poor long-term cycle stability.

[0003] Among numerous anode materials, binary transition metal oxides (BMOs) have a broader application prospect compared to other oxide anode materials due to their higher reversible capacity, better structural stability, and high electronic conductivity. Ferrous titanate (FeTiO3), as a novel BMO anode material, possesses high theoretical capacity and cycling stability. Furthermore, FeTiO3 exhibits a unique [BO6] octahedral structure, which endows it with rich physicochemical properties. As an electrode material, FeTiO3 simultaneously possesses both intercalation and conversion lithium storage mechanisms during cycling. This "dual-mechanism synergy" characteristic results in fast kinetics and good reversibility in its intercalation reaction. However, the low electronic conductivity and ion mobility of FeTiO3 limit its stability during cycling.

[0004] A heterojunction is a structure formed by coupling two or more semiconductor materials with different band gaps. Constructing this heterogeneous structure is extremely effective in improving the conductivity of materials. A potential difference is generated at the interface of a heterojunction, causing a redistribution of charges and forming an internal electric field. The energy barrier for ions and electrons during transport within this internal electric field is significantly reduced, thereby improving the material's charge transport capability.

[0005] Patent CN117374262A discloses an intrinsic heterojunction anode material and its preparation method. Using graphene oxide as a substrate, the crosslinking properties of a crosslinking agent are utilized to sinter an intrinsic heterojunction composed of FeTiO3 and Fe2TiO5 under a reducing atmosphere, which can improve the conductivity of the electrode material itself and obtain an excellent anode material. However, this FeTiO3@Fe2TiO5 intrinsic heterojunction and its preparation method still have the following drawbacks: the preparation process is relatively complex, and the heterojunction is directly generated under a reducing atmosphere, making the product uncontrollable. Therefore, it is necessary to construct new ferrous titanate heterojunctions to solve the technical problems of poor lithium storage performance, electrochemical performance, and cycle stability of existing ferrous titanate anode materials. Summary of the Invention

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

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] A FeTiO3-BiFeO3 heterojunction is formed by ferrous titanate and bismuth ferrite in a mass ratio of 1:(0.5-2) to form a pn heterojunction structure.

[0009] A method for preparing a FeTiO3-BiFeO3 heterojunction includes the following steps:

[0010] Step (1): Using tetrabutyl titanate as the titanium source and soluble ferrous salt as the iron source, ferrous titanate is prepared by hydrothermal synthesis to obtain ferrous titanate powder.

[0011] Step (2): Using bismuth salt as the bismuth source and soluble ferric salt as the iron source, bismuth ferrite is prepared by hydrothermal synthesis to obtain bismuth ferrite powder;

[0012] Step (3): Add ferrous titanate powder to water and ultrasonically disperse it evenly, then add bismuth ferrite powder and continue ultrasonic dispersion. After ultrasonic dispersion is completed, continue stirring until the two powders are mixed and dispersed evenly to obtain a mixed dispersion.

[0013] Step (4): Place the mixed dispersion in a reaction vessel for hydrothermal reaction. After the reaction is completed, separate the solid and liquid. Wash and dry the separated solid precipitate to obtain the above FeTiO3-BiFeO3 heterojunction.

[0014] Compared with conventional sol-gel and solid-phase methods, the ferrous titanate and bismuth ferrite synthesized by the hydrothermal synthesis method of this invention have better crystallinity and superior electrocycle performance when used as electrode materials alone. When the two are further prepared by the hydrothermal synthesis method of this invention, the FeTiO3-BiFeO3 heterojunction is used as an electrode material, and its electrocycle performance is significantly improved.

[0015] In the above method for preparing FeTiO3-BiFeO3 heterojunctions, step (1) involves the following preparation method for ferrous titanate powder:

[0016] Step (1-1): Add tetrabutyl titanate dropwise to tetrabutylammonium hydroxide solution to obtain mixture A;

[0017] Steps (1-2): Heat and stir mixture A until it becomes transparent, then add ferrous sulfate solution and continue heating and stirring. Then, while heating and stirring, add potassium hydroxide and stir until well mixed to obtain mixture B.

[0018] Steps (1-3): Place the mixture B in a reaction vessel for hydrothermal reaction. After the reaction is completed, separate the solid and liquid. Wash and dry the separated solid precipitate to obtain ferrous titanate powder.

[0019] In the above method for preparing FeTiO3-BiFeO3 heterojunction, in step (1-1), the volume ratio of tetrabutylammonium hydroxide to water in the tetrabutylammonium hydroxide solution is 1:(10-12). The pH of the tetrabutylammonium hydroxide solution at this concentration is moderate, which is conducive to the subsequent reaction to generate ferrous titanate. The volume ratio of the total volume of tetrabutyl titanate to the volume of tetrabutylammonium hydroxide is 1:(1.5-2.0). The dropping rate of tetrabutyl titanate is 1.0-1.5 mL / min. By controlling the dropping rate of tetrabutyl titanate into tetrabutylammonium hydroxide and the volume ratio of the total amount of tetrabutyl titanate to the volume of tetrabutylammonium hydroxide, the tetrabutyl titanate can be fully hydrolyzed in the mixed solution A, avoiding the formation of white flocculent precipitate.

[0020] In steps (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, continue heating and stirring for 20-30 min, and after adding potassium hydroxide, continue heating and stirring for 10-15 min; throughout the entire process of steps (1-2), the heating and stirring temperature is 60-70℃, and the heating and stirring rate is 400-500 rpm; by controlling the concentration and amount of ferrous sulfate solution and the amount of potassium hydroxide, the ratio of titanium source and iron source in mixture B is adjusted to a suitable range, and the heating and stirring temperature and rate are controlled throughout the entire process of steps (1-2), which can effectively avoid the oxidation and decomposition of the effective components in the system, reduce the generation of impurities such as iron(III) oxide during the preparation of ferrous titanate, and thus ensure the purity of the target product;

[0021] In steps (1-3), the hydrothermal reaction temperature is 210–230℃, and the hydrothermal reaction time is 10–16 h. If the hydrothermal reaction temperature is below 210℃, the iron source will generate a magnetite impurity phase; if the hydrothermal reaction temperature is above 230℃, a titanium dioxide impurity phase will be generated. This invention, by controlling the hydrothermal reaction temperature and the hydrothermal reaction time within the range of 10–16 h, enables the titanium and iron sources in the reaction system to fully react and generate ferrous titanate, reducing the generation of magnetite and titanium dioxide impurities, ensuring the purity of the target product, and providing a foundation for the subsequent preparation of FeTiO3-BiFeO3 heterojunctions. During washing, deionized water and anhydrous ethanol are used for repeated washing 3–5 times. The drying conditions are: drying at 70–80℃ for 10–16 h. Under these drying conditions, moisture can be fully removed, and the oxidation of ferrous titanate can be effectively avoided.

[0022] The preparation method of the above FeTiO3-BiFeO3 heterojunction and the preparation method of bismuth ferrite powder are as follows:

[0023] Step (2-1): Add bismuth salt and soluble ferric salt to an inorganic acid solution and stir to dissolve, to obtain mixture C;

[0024] Step (2-2): Add potassium hydroxide solution A dropwise into mixed solution C until the precipitation reaction is complete to obtain a mixed reaction system; sonicate the mixed reaction system and stir to mix it evenly, and then perform solid-liquid separation; wash 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;

[0025] Step (2-3): The solid intermediate product is redispersed in potassium hydroxide solution B, ultrasonically treated and stirred to obtain mixture D;

[0026] Step (2-4): Place the mixture D in a reaction vessel for hydrothermal reaction. After the reaction is completed, separate the solid and liquid. Wash and dry the separated solid precipitate to obtain bismuth ferrite powder.

[0027] In the above method for preparing 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 5-10%; in the mixed solution C, the molar ratio of soluble bismuth salt to soluble trivalent iron salt is (1.0-1.5):1 (when the molar ratio of the two salts is within this range, the generation of other impurities besides bismuth ferrite can be effectively reduced), and the molar concentration of soluble trivalent iron salt is 0.2-0.4 mol / L; by controlling the volume fraction of the dilute nitric acid solution and the molar concentrations of iron salt and bismuth salt in the mixed solution C, the bismuth salt and iron salt can be fully dissolved and completely dissociated in the mixed solution C, which is beneficial for the subsequent full reaction to synthesize bismuth ferrite;

[0028] In step (2-2), the molar concentration of potassium hydroxide solution A is 1–4 mol / L; the amount of potassium hydroxide solution A added is controlled so that the pH of the mixed reaction system is 10–12; the ultrasonic treatment time is 10–15 min, the stirring and mixing time is 20–30 min, and the stirring speed is 400–500 rpm; by controlling the pH of the mixed reaction system within a specific range, the intermediate reaction can be ensured to proceed fully.

[0029] In steps (2-3), the molar concentration of potassium hydroxide solution B is 5-10 mol / L; in the mixed solution D, the molar ratio of iron to potassium hydroxide is 1:(60-90); the ultrasonic treatment time is 10-15 min, the stirring and mixing time is 20-30 min, and the stirring speed is 400-500 rpm.

[0030] In steps (2-4), the hydrothermal reaction temperature is 230–250℃, and the hydrothermal reaction time is 10–16 h. If the hydrothermal reaction temperature is below 230℃, a Bi2Fe4O9 impurity phase will be formed. If the hydrothermal reaction temperature is above 250℃, or the hydrothermal reaction time exceeds the above range, the purity of the final bismuth ferrite powder will decrease. During washing, deionized water and anhydrous ethanol are used to wash repeatedly 3–5 times. The drying conditions are: drying at 70–80℃ for 10–16 h. These drying conditions can thoroughly dry the bismuth ferrite powder without causing the bismuth ferrite to decompose.

[0031] In the above method for preparing FeTiO3-BiFeO3 heterojunction, in step (3), the particle size range of ferrous titanate powder is 0.05-0.10 μm, and the particle size range of bismuth ferrite powder is 0.05-0.10 μm; the time for the two ultrasonic dispersions is 10-15 min each; after the second ultrasonic dispersion, stirring is continued for 20-30 min at a stirring rate of 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.

[0032] In the above method for preparing FeTiO3-BiFeO3 heterojunction, in step (4), the hydrothermal reaction temperature is 150-180℃ and the hydrothermal reaction time is 10-16h. Under these reaction conditions, ferrous titanate and bismuth ferrite of a specific particle size can fully react to generate 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 to wash repeatedly 3-5 times. The drying conditions are: drying at 70-80℃ for 10-16h.

[0033] In the above method for preparing FeTiO3-BiFeO3 heterojunctions, step (1) involves the following preparation method for ferrous titanate powder:

[0034] Step (1-1): Tetrabutyl titanate is added dropwise to a tetrabutylammonium hydroxide solution to obtain mixture A; the volume ratio of tetrabutylammonium hydroxide to water in the tetrabutylammonium hydroxide solution is 1:11.5; the total volume ratio of the added tetrabutyl titanate to the tetrabutylammonium hydroxide is 1:1.8; the dropping rate of tetrabutyl titanate is 1.0 mL / min;

[0035] Steps (1-2): After heating and stirring mixture A at 60°C until transparent, add ferrous sulfate solution with a molar concentration of 1.5 mol / L and continue heating and stirring for 30 min. Then add potassium hydroxide and heat and stir for 10 min to mix thoroughly, obtaining mixture 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 speed in this step is 450 rpm.

[0036] Steps (1-3): Place the mixture B in a reaction vessel and hydrothermally react at 220℃ for 12 hours. After the reaction is completed, separate the solid and liquid. Wash the separated solid precipitate repeatedly with deionized water and anhydrous ethanol three times, and then dry it at 80℃ for 12 hours to obtain ferrous titanate powder.

[0037] The preparation method of bismuth ferrite powder is as follows:

[0038] Step (2-1): Add bismuth nitrate pentahydrate and ferric nitrate nonahydrate to a 10% (v / v) dilute nitric acid solution in a molar ratio of 1.2:1 and stir to dissolve, to obtain mixture C; the molar concentration of ferric nitrate nonahydrate in mixture C is 0.25 mol / L.

[0039] Step (2-2): Add a 2 mol / L potassium hydroxide solution A dropwise to the mixed solution C until the precipitation reaction is complete, obtaining a mixed reaction system. Control the amount of potassium hydroxide solution A added to ensure that the pH of the mixed reaction system is 11. Sonicate the mixed reaction system for 10 min and stir for 30 min at a stirring rate of 450 rpm, then separate the solid and liquid. Wash the separated solid precipitate with deionized water until neutral to obtain a solid intermediate product.

[0040] Step (2-3): The solid intermediate product is redispersed in an 8 mol / L potassium hydroxide solution B, ultrasonicated for 10 min and stirred for 30 min at a stirring rate of 450 rpm to obtain a mixture D; in the mixture D, the molar ratio of iron to potassium hydroxide is 1:80.

[0041] Step (2-4): Place the mixture D in a reaction vessel and hydrothermally react at 240℃ for 12 hours. After the reaction is completed, separate the solid and liquid. Wash the separated solid precipitate repeatedly with deionized water and anhydrous ethanol three times, and then dry it at 80℃ for 12 hours to obtain bismuth ferrite powder.

[0042] In step (3), the particle size range of ferrous titanate powder is 0.05-0.10 μm, and the particle size range of bismuth ferrite powder is 0.05-0.10 μm; the ultrasonic dispersion time is 10 min for both times; after the second ultrasonic dispersion, stirring is continued for 30 min at a stirring rate of 450 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 0.033 mol / L;

[0043] In step (4), the hydrothermal reaction temperature is 160℃ and the hydrothermal reaction time is 12h; during washing, deionized water and anhydrous ethanol are used to wash repeatedly 3 times; the drying conditions are: drying at 80℃ for 12h.

[0044] An application of FeTiO3-BiFeO3 heterojunction: The above-mentioned FeTiO3-BiFeO3 heterojunction will be used to prepare the anode material for lithium batteries.

[0045] The technical solution of the present invention achieves the following beneficial technical effects:

[0046] 1. The present invention provides a method for preparing FeTiO3-BiFeO3 heterojunctions. The FeTiO3-BiFeO3 heterojunction structure was successfully constructed by a stepwise hydrothermal method. The method is simple to operate, has a fast synthesis speed, and the synthesized components are stable. The prepared FeTiO3-BiFeO3 p-n heterojunction can be used as an anode material for lithium batteries. The FeTiO3-BiFeO3 heterojunction structure prepared by the method of this invention can form a heterogeneous interface between FeTiO3 and BiFeO3, thereby generating a certain potential difference at the interface and forming an internal electric field. This invention selects a hydrothermal synthesis method to prepare FeTiO3 and BiFeO3 separately. By controlling the hydrothermal synthesis process parameters, the crystallinity of the prepared FeTiO3 and BiFeO3 can be significantly improved. Further hydrothermal synthesis, by controlling the ratio of the two and the hydrothermal synthesis process parameters, results in a FeTiO3-BiFeO3 heterojunction with a high electronic state density and a low ion diffusion barrier, greatly improving its ion transport efficiency. Simultaneously, the unique heterojunction structure of the FeTiO3-BiFeO3 prepared by this invention can also effectively improve the lithium storage capacity of the material itself, effectively inhibit the decomposition of effective substances in FeTiO3 during cycling, and greatly improve the stability of the electrode material.

[0047] 2. In the FeTiO3-BiFeO3 heterojunction prepared in this invention, BiFeO3, as a Fe-based binary transition metal oxide similar to FeTiO3, also has a stable perovskite structure, and both belong to the rhombohedral crystal system. Simultaneously, FeTiO3 and BiFeO3 are n-type and p-type semiconductors, respectively, and electron movement is achieved through electron / hole transitions. A corresponding pn heterostructure is formed at their interface, thereby promoting charge transfer and improving lithium-ion adsorption. Therefore, this unique heterojunction structure can effectively improve the lithium storage performance and electrochemical performance of the material itself. Furthermore, the built-in electric field of this FeTiO3-BiFeO3 heterojunction enables charge redistribution, effectively reducing the diffusion resistance of ions and charges, increasing carrier concentration, and thus significantly improving the cycle performance of the battery.

[0048] 3. This invention uses tetrabutyl titanate as the titanium source and ferrous sulfate as the iron source to prepare ferrous titanate via hydrothermal synthesis. 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 throughout the preparation process, the prepared ferrous titanate can achieve ideal crystallinity. Compared with conventional sol-gel and solid-phase methods, it exhibits superior electrocycling performance as an electrode material. This invention also uses bismuth pentahydrate as the bismuth source and ferric nitrate nonahydrate as the iron source to prepare bismuth ferrite via hydrothermal synthesis. By controlling the proportions of raw materials and reaction parameters during the preparation process, the crystallinity of the obtained bismuth ferrite can be significantly optimized, improving its electrocycling performance as an electrode material. The ferrous titanate and bismuth ferrite prepared by the hydrothermal synthesis method of the present invention are then 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. Attached Figure Description

[0049] Figure 1 XRD comparison images of different anode materials in the embodiments of the present invention;

[0050] Figure 2 TEM morphology of the FeTiO3-1BiFeO3 heterojunction prepared in the embodiments of the present invention;

[0051] Figure 3 HRTEM morphology of the FeTiO3-1BiFeO3 heterojunction prepared in the embodiments of the present invention;

[0052] Figure 4 Cycle capacity diagram of batteries assembled with different anode materials in embodiments of the present invention (current magnitude 0.1 Ag). -1 );

[0053] Figure 5 The constant current charge-discharge curve of the battery assembled using the prepared FeTiO3-2BiFeO3 heterojunction as the anode material in this embodiment of the invention (current magnitude is 0.1 A g) is shown. -1 );

[0054] Figure 6 The constant current charge-discharge curve of the battery assembled using the prepared FeTiO3-1BiFeO3 heterojunction as the anode material in this embodiment of the invention (current magnitude is 0.1 A g) is shown. -1 );

[0055] Figure 7The constant current charge-discharge curves (current magnitude 0.1 A g) of the battery assembled using the prepared FeTiO3-0.5BiFeO3 heterojunction as the anode material in this embodiment of the invention are shown. -1 );

[0056] Figure 8 Cycle capacity diagram of batteries assembled with different anode materials in embodiments of the present invention (current magnitude 1.0 Ag). -1 );

[0057] Figure 9 Charge-discharge curves of batteries assembled with different anode materials in embodiments of the present invention (current ranges from 0.1 to 2.0 A g). -1 );

[0058] Figure 10 The CV curves (scan rates ranging from 0.1 mV to 2 mV) of the battery assembled using the prepared FeTiO3-1BiFeO3 heterojunction as the anode material in this embodiment of the invention are shown.

[0059] Figure 11 In this embodiment of the invention, the fitting curves of the peak current versus the square root of the scan rate of the battery assembled using the prepared FeTiO3 and FeTiO3-1BiFeO3 heterojunction as the anode material at different scan rates are shown.

[0060] Figure 12 The fitted curves of the peak current logarithm and the logarithm of the sweep rate of the battery assembled with the prepared FeTiO3-1BiFeO3 heterojunction as the anode material at different sweep rates in the embodiments of the present invention.

[0061] Figure 13 Pseudocapacitance contribution diagrams of batteries assembled using the prepared FeTiO3-1BiFeO3 heterojunction as the anode material at different scan rates in this embodiment of the invention.

[0062] Figure 14 Quest impedance diagram of a battery assembled using the prepared FeTiO3-1BiFeO3 heterojunction as the anode material in an embodiment of the present invention;

[0063] Figure 15 Cycle capacity diagrams (current magnitude 1.0 A g) of batteries assembled using BiFeO3 samples prepared in this embodiment of the invention and BiFeO3 samples prepared by conventional sol-gel and solid-phase methods as anode materials. -1 );

[0064] Figure 16 TEM morphology of the FeTiO3-2BiFeO3 heterojunction prepared in the embodiments of the present invention;

[0065] Figure 17HRTEM morphology of the FeTiO3-2BiFeO3 heterojunction prepared in the embodiments of the present invention;

[0066] Figure 18 TEM morphology image of the FeTiO3-0.5BiFeO3 heterojunction prepared in the embodiments of the present invention;

[0067] Figure 19 HRTEM morphology of the FeTiO3-0.5BiFeO3 heterojunction prepared in this embodiment of the invention. Detailed Implementation

[0068] The preparation method of FeTiO3-BiFeO3 heterojunction in this embodiment includes the following steps:

[0069] 1. Preparation of FeTiO3 powder

[0070] Measure 5.2 mL of tetrabutylammonium hydroxide and add it to a beaker containing 60 mL of deionized water, stirring for 10 min. Measure 2.818 mL of tetrabutyl titanate and slowly add it dropwise (at a dropping rate of 1.0 mL / min) to the above mixture, then transfer it to a water bath and heat and stir at 60 °C (stirring rate 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 above transparent liquid and continue heating and stirring at 450 rpm for 30 min. Then add 2 g of KOH solid powder and continue heating and stirring at 450 rpm for 10 min. Transfer the resulting mixture to a 100 mL reactor and keep it at 220 °C for 12 h. After the reaction is complete, the solid and liquid are separated. The obtained solid precipitate is washed three times with deionized water and ethanol, and then dried in an oven at 80°C for 12 h to obtain FeTiO3 powder. The powder is then ground to a particle size of 0.05–0.10 μm for later use.

[0071] 2. Preparation of BiFeO3 powder

[0072] 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 2M KOH solution and slowly add it dropwise to the above mixed solution. At this time, a large amount of orange-yellow precipitate will be produced and the color will gradually darken. Continue to add KOH solution and adjust the pH value to 11 to allow the mixture to precipitate completely. Sonicate the mixed reaction system for 10 min and then stir rapidly at a stirring rate of 450 rpm for 30 min to uniformly disperse the precipitate. Wash repeatedly with deionized water and centrifuge until the precipitate is neutral. Then add 50 mL of 8M KOH solution to the precipitate, sonicate for 10 min, and stir rapidly at a stirring rate of 450 rpm for 30 min. Transfer the resulting solution to a 100 mL reaction vessel and keep it at 240℃ for 12 h. The precipitate was washed three times with deionized water and ethanol, and dried in an oven at 80°C for 12 h to obtain BiFeO3 powder. The BiFeO3 powder was then ground to a particle size of 0.05–0.10 μm for later use.

[0073] 3. Preparation of FeTiO3-BiFeO3

[0074] Weigh FeTiO3 powder and BiFeO3 powder in mass ratios of 2:1, 1:1, and 1:2. Add 60 mL of deionized water to the FeTiO3 powder and sonicate for 10 min. Then add the BiFeO3 powder to the dispersion and sonicate for another 10 min. Stir rapidly at 450 rpm for 30 min to ensure uniform dispersion. Place the resulting mixture in a 100 mL reactor and incubate at 160℃ for 12 h. After the reaction, separate the solid and liquid phases. Wash the resulting solid precipitate three times with deionized water and ethanol, and dry it in an oven at 80℃ for 12 h to obtain FeTiO3-BiFeO3 powder. Grind the powder through a 450-mesh sieve for later use. FeTiO3-BiFeO3 powders prepared from 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.

[0075] Lithium-ion battery anodes were prepared using FeTiO3-0.5BiFeO3, FeTiO3-1BiFeO3, and FeTiO3-2BiFeO3, and batteries were assembled. The performance of each electrode material was then tested.

[0076] Battery assembly method: First, the electrode materials and acetylene black are thoroughly ground and mixed in a mortar. Then, sodium alginate (SA) is added and further ground and mixed, with a ratio of 8:1:1. Deionized water is added dropwise to prepare a slurry. The slurry is then coated onto a special copper foil for the anode and dried in a vacuum drying oven at 80 °C for 12 h. After drying, it is removed and cut. The electrolyte consists of 1 mol / L LiPF6 and EC:DMC:DEC (volume ratio 1:1:1). A polypropylene (PP) microporous membrane is used as the separator, and lithium metal sheets are used as electrodes. Finally, the 2032 button cell is assembled in an argon-protected glove box.

[0077] Performance testing method: Connect the assembled electrode sheet to the Blue Electricity testing system, set the voltage window to 0.01~3V, and select a current density of 0.1 A g. -1 Test the constant current charge-discharge cycle. Continue to set the current density to 0.1 A g⁻¹ to 2 A g⁻¹. -1 Test the rate charge-discharge cycle.

[0078] from Figure 1 As can be seen from the comparison with the PDF card (PDF#22-0169), diffraction peaks corresponding to the (110), (211), (210), (220), and (321) crystal planes of FeTiO3 were observed at 2θ values ​​of 23.87°, 32.53°, 40.52°, 48.91°, and 53.24°, respectively. The characteristic peaks observed at 2θ values ​​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.

[0079] from Figure 2 It can be seen that the FeTiO3-1BiFeO3 sample exhibits a relatively obvious hexagonal structure, with some overlap at the interface.

[0080] from Figure 3 As can be seen, the HRTEM image clearly shows 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, which indicates the successful synthesis of the heterojunction structure.

[0081] The microstructures of the FeTiO3-0.5BiFeO3 and FeTiO3-2BiFeO3 heterojunctions are quite similar to those of the FeTiO3-1BiFeO3 heterojunction, such as... Figures 16 to 19As shown in the figure, the FeTiO3-0.5BiFeO3 and FeTiO3-2BiFeO3 samples synthesized in this embodiment also exhibit heterojunction structures.

[0082] from Figure 4 It can be seen that FeTiO3-1BiFeO3 exhibits a maximum energy density of 984.1 mAh g after 250 cycles of the test. -1 The high capacity performance of FeTiO3 was achieved, while the capacity of FeTiO3 decreased to 631.5 mAh g. -1 The BiFeO3 capacity decreased to 484 mAh g. -1 .

[0083] from Figures 5 to 7 It can be seen that the charge-discharge plateau of the FeTiO3-BiFeO3 constant current charge-discharge curve changed significantly with different proportions.

[0084] from Figure 8 It can be seen that in 1 Ag -1 At the specified current density, FeTiO3-1BiFeO3 exhibits a capacity of 268.7 mAh g after 1000 cycles. -1 Still superior to FeTiO3 (59mAh g) -1 ) and BiFeO3 (26mAh g) -1 It exhibits good cyclic stability.

[0085] 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.

[0086] In summary, compared with the FeTiO3-0.5BiFeO3 and FeTiO3-2BiFeO3 heterojunctions, the anode material prepared by the FeTiO3-1BiFeO3 heterojunction exhibits better electrochemical performance. Further performance tests were conducted on the batteries assembled using it.

[0087] from Figures 10 to 13 As can be seen, the CV curves at each scan rate show a similar trend with no obvious polarization phenomenon. During cycling, the electrode material exhibits both battery properties and pseudocapacitive properties. This indicates that the construction of the heterojunction improves the lithium-ion diffusion coefficient of the sample, promotes lithium-ion transport efficiency, and thus improves the battery's cycling performance; with the increase of scan rate, the contribution of pseudocapacitance also increases.

[0088] from Figure 14It can be seen that, through the construction of the heterojunction structure, the FeTiO3-1BiFeO3 sample has a significantly higher electrolyte resistance compared to the FeTiO3 sample. R e ) and charge transfer impedance ( R ct The value of ) decreases significantly, and the significant reduction in diffusion resistance (W0-R) corresponds to the increase in ion diffusion coefficient.

[0089] Figure 15 The figure shows the electrocycling performance of BiFeO3 samples prepared by different methods as electrode materials. As can be seen from the figure, the BiFeO3 sample synthesized by the hydrothermal method in this embodiment exhibits better electrocycling performance than the conventional sol-gel method and solid-phase method.

[0090] In summary, this invention first prepared a FeTiO3-BiFeO3 heterojunction anode material via hydrothermal synthesis. This material exhibits lower internal resistance and a higher ion diffusion coefficient, and its superior electrochemical performance is attributed to its unique heterojunction structure. The built-in electric field formed by the construction of this heterojunction structure leads to a redistribution of electrons within the material, significantly reducing the diffusion resistance of ions and charges, thereby significantly improving the material's electrical properties. Simultaneously, due to the formation of the interface, the material structure is more stable and less prone to structural collapse at high current densities, greatly improving the material's cycling performance. Compared to previously reported FeTiO3 and BiFeO3 anode materials, at a current density of 0.1 A g... -1 After 250 cycles, the capacity decay of the FeTiO3-BiFeO3 sample was significantly reduced to 984.1 mAh g. -1 Under high current long-cycle conditions (1A g) -1 The capacity of the FeTiO3-BiFeO3 sample was 268.7 mAh g after 1000 cycles at the current density. -1 .

[0091] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing a FeTiO3-BiFeO3 heterojunction, characterized in that, The FeTiO3-BiFeO3 heterojunction is formed by ferrous titanate and bismuth ferrite in a mass ratio of 1:(0.5~2) to form a pn heterojunction structure. The preparation method includes the following steps: Step (1): Using tetrabutyl titanate as the titanium source and soluble ferrous salt as the iron source, ferrous titanate is prepared by hydrothermal synthesis to obtain ferrous titanate powder. Step (2): Using bismuth salt as the bismuth source and soluble ferric salt as the iron source, bismuth ferrite is prepared by hydrothermal synthesis to obtain bismuth ferrite powder; Step (3): Add ferrous titanate powder to water and ultrasonically disperse it evenly, then add bismuth ferrite powder and continue ultrasonic dispersion. After ultrasonic dispersion, continue stirring until the two powders are mixed and dispersed evenly to obtain a mixed dispersion. In the mixed dispersion, the mass ratio of ferrous titanate to bismuth ferrite is 1:(0.5~2). Step (4): Place the mixed dispersion in a reaction vessel for hydrothermal reaction at a temperature of 150-180°C. After the reaction is completed, separate the solid and liquid components. The separated solid precipitate was washed and dried to obtain FeTiO3-BiFeO3 heterojunction.

2. The method for preparing FeTiO3-BiFeO3 heterojunction according to claim 1, characterized in that, In step (1), the preparation method of ferrous titanate powder is as follows: Step (1-1): Add tetrabutyl titanate dropwise to tetrabutylammonium hydroxide solution to obtain mixture A; Steps (1-2): Heat and stir mixture A until it becomes transparent, then add ferrous sulfate solution and continue heating and stirring. Then, while heating and stirring, add potassium hydroxide and stir until well mixed to obtain mixture B. Steps (1-3): Place the mixture B in a reaction vessel for hydrothermal reaction. After the reaction is completed, separate the solid and liquid. Wash and dry the separated solid precipitate to obtain ferrous titanate powder.

3. The method for preparing FeTiO3-BiFeO3 heterojunction according to claim 2, characterized in that, In step (1-1), the volume ratio of tetrabutylammonium hydroxide to water in the tetrabutylammonium hydroxide solution is 1:(10-12); the volume ratio of the total volume of tetrabutyl titanate to the volume of tetrabutylammonium hydroxide is 1:(1.5-2.0); and the dropping rate of tetrabutyl titanate is 1.0-1.5 mL / min. In steps (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, continue heating and stirring for 20-30 min, and after adding potassium hydroxide, continue heating and stirring for 10-15 min; throughout the entire process of steps (1-2), the heating and stirring temperature is 60-70℃, and the heating and stirring rate is 400-500 rpm; In steps (1-3), the hydrothermal reaction temperature is 210-230℃ and the hydrothermal reaction time is 10-16h; during washing, deionized water and anhydrous ethanol are used to wash repeatedly 3-5 times; the drying conditions are: drying at 70-80℃ for 10-16h.

4. The method for preparing FeTiO3-BiFeO3 heterojunction according to claim 1, characterized in that, The preparation method of bismuth ferrite powder is as follows: Step (2-1): Add bismuth salt and soluble ferric salt to an inorganic acid solution and stir to dissolve, to obtain mixture C; Step (2-2): Add potassium hydroxide solution A dropwise into mixed solution C until the precipitation reaction is complete to obtain a mixed reaction system; sonicate the mixed reaction system and stir to mix it evenly, and then perform solid-liquid separation; wash the separated solid precipitate with deionized water until neutral to obtain a solid intermediate product; Step (2-3): The solid intermediate product is redispersed in potassium hydroxide solution B, ultrasonically treated and stirred to obtain mixture D; Step (2-4): Place the mixture D in a reaction vessel for hydrothermal reaction. After the reaction is completed, separate the solid and liquid. Wash and dry the separated solid precipitate to obtain bismuth ferrite powder.

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

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

7. The method for preparing FeTiO3-BiFeO3 heterojunction according to claim 1, characterized in that, In step (4), the hydrothermal reaction time is 10-16 h; during washing, deionized water and anhydrous ethanol are used to wash repeatedly 3-5 times; the drying conditions are: drying at 70-80℃ for 10-16 h.

8. The method for preparing FeTiO3-BiFeO3 heterojunction according to claim 1, characterized in that, In step (1), the preparation method of ferrous titanate powder is as follows: Step (1-1): Tetrabutyl titanate is added dropwise to a tetrabutylammonium hydroxide solution to obtain mixture A; the volume ratio of tetrabutylammonium hydroxide to water in the tetrabutylammonium hydroxide solution is 1:11.5; the total volume ratio of the added tetrabutyl titanate to the tetrabutylammonium hydroxide is 1:1.8; the dropping rate of tetrabutyl titanate is 1 mL / min. Steps (1-2): Heat and stir mixture A at 60°C until transparent, then add ferrous sulfate solution with a molar concentration of 1.5 mol / L and continue stirring for 30 min. Then add potassium hydroxide and stir for 10 min to mix thoroughly, obtaining mixture B. The volume ratio of ferrous sulfate solution to mixture A is 1:6.8, and the molar ratio of potassium hydroxide to ferrous sulfate is 2.4:

1. The stirring speed in this step is 450 rpm. Steps (1-3): Place the mixture B in a reaction vessel and hydrothermally react at 220℃ for 12 hours. After the reaction is completed, separate the solid and liquid. Wash the separated solid precipitate repeatedly with deionized water and anhydrous ethanol three times, and then dry it at 80℃ for 12 hours to obtain ferrous titanate powder. The preparation method of bismuth ferrite powder is as follows: Step (2-1): Add bismuth nitrate pentahydrate and ferric nitrate nonahydrate to a 10% (v / v) dilute nitric acid solution in a molar ratio of 1.2:1 and stir to dissolve, to obtain mixture C; the molar concentration of ferric ions is 0.25 mol / L. Step (2-2): Add a 2 mol / L potassium hydroxide solution A dropwise to the mixed solution C until the precipitation reaction is complete, obtaining a mixed reaction system. Control the amount of potassium hydroxide solution A added to ensure that the pH of the mixed reaction system is 11. Sonicate the mixed reaction system for 10 min and stir for 30 min at a stirring rate of 450 rpm, then separate the solid and liquid. Wash the separated solid precipitate with deionized water until neutral to obtain a solid intermediate product. Step (2-3): The solid intermediate product is redispersed in an 8 mol / L potassium hydroxide solution B, ultrasonicated for 10 min and stirred for 30 min at a stirring rate of 450 rpm to obtain a mixture D; in the mixture D, the molar ratio of iron to potassium hydroxide is 1:

80. Step (2-4): Place the mixture D in a reaction vessel and hydrothermally react at 240℃ for 12 hours. After the reaction is completed, separate the solid and liquid. Wash the separated solid precipitate repeatedly with deionized water and anhydrous ethanol three times, and then dry it at 80℃ for 12 hours to obtain bismuth ferrite powder. In step (3), the particle size range of ferrous titanate powder is 0.1-0.3 μm, and the particle size range of bismuth ferrite powder is 0.1-0.3 μm; the ultrasonic dispersion time is 10 min for both times; after the second ultrasonic dispersion, stirring is continued for 30 min at a stirring rate of 450 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 0.033 mol / L; In step (4), the hydrothermal reaction temperature is 160℃ and the hydrothermal reaction time is 12h; during washing, deionized water and anhydrous ethanol are used to wash repeatedly 3 times; the drying conditions are: drying at 80℃ for 12h.

9. An application of a FeTiO3-BiFeO3 heterojunction, characterized in that, The FeTiO3-BiFeO3 heterojunction prepared by the method described in any one of claims 1-8 will be used to prepare the anode material for lithium batteries.

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