{001} Anatase Titanium Dioxide Nanosheets with Exposed Crystal Facets, Preparation Methods, and Applications

Abstract

This invention relates to battery materials technology, catalysis, and sensors, specifically to anatase titanium dioxide nanosheets with exposed {001} crystal faces, their preparation method, and applications. The method includes: adding a titanium source to a hydrofluoric acid solution and mixing and stirring to obtain a reaction precursor; transferring the reaction precursor to a reaction vessel for hydrothermal reaction; after the reaction, cooling, separating, washing, and drying to obtain anatase titanium dioxide nanosheets with exposed {001} crystal faces. The preparation process is simple and efficient, and the obtained anatase titanium dioxide nanosheets have high purity, large specific surface area, and high surface energy, making them suitable as cathode materials for magnesium-ion batteries and magnesium-lithium hybrid batteries.

Description

Technical Field

[0001] This invention relates to battery materials technology, catalysis, and sensors, specifically to anatase titanium dioxide nanosheets with exposed {001} crystal faces, their preparation method, and applications. Background Technology

[0002] Compared to mainstream lithium-ion batteries, rechargeable magnesium-ion batteries (MIBs) possess advantages such as abundant magnesium reserves, low cost, high theoretical volumetric energy density, low electrode potential, and higher safety, making them one of the most promising technologies for large-scale application and a candidate battery for the post-lithium-ion battery era. Despite these potential advantages, the strong polarization effect of divalent magnesium ions hinders the rapid insertion / extraction of magnesium ions into the cathode material, and may even inhibit reversible insertion, resulting in strong polarization and poor electrochemical behavior during charging and discharging. This drawback presents significant challenges for magnesium-ion batteries.

[0003] To date, research on magnesium rechargeable batteries has been limited to a few electrode materials, such as vanadium oxide, Chevrell phases, molybdenum sulfide, manganese oxide, and transition metal silicates. However, the sluggish kinetics of magnesium ion diffusion limit the magnesium ion intercalation capability of these materials. Titanium dioxide is a naturally abundant, non-toxic material that is easy to prepare and possesses high chemical stability, and has been extensively studied in various fields such as photocatalysis and lithium-ion batteries. Anatase titanium dioxide, with its tetragonal crystal structure, is perhaps the most studied metal oxide. Given the widespread application of anatase titanium dioxide in lithium-ion and sodium-ion batteries, it is also considered a promising electrode material for magnesium-ion batteries. However, the discharge capacity of the magnesium / anatase titanium dioxide prototype system in magnesium-ion batteries is still insufficient for various applications. Summary of the Invention

[0004] The purpose of this invention is to provide anatase titanium dioxide nanosheets with exposed {001} crystal planes, a preparation method, and applications. The preparation process is simple and efficient, and the resulting anatase titanium dioxide nanosheets have high purity, large specific surface area, and high surface energy, making them suitable as cathode materials for magnesium-ion batteries and magnesium-lithium hybrid batteries.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing anatase titanium dioxide nanosheets with exposed {001} crystal faces, the method comprising: adding a titanium source to a hydrofluoric acid solution and mixing and stirring to obtain a reaction precursor; transferring the reaction precursor to a reaction vessel for hydrothermal reaction; and after the reaction is completed, cooling, separating, washing and drying to obtain anatase titanium dioxide nanosheets with exposed {001} crystal faces.

[0006] Furthermore, 3-6 mL of titanium source is added to every 0.3-1.6 mL of hydrofluoric acid solution with a concentration of ~47%; the titanium source includes tetrabutyl titanate, titanium tetrachloride, or isopropyl titanate.

[0007] Furthermore, the hydrothermal reaction temperature is 100~200℃, and the hydrothermal reaction time is 16~24 hours.

[0008] Furthermore, the thickness of the obtained anatase titanium dioxide nanosheets with exposed {001} crystal planes ranges from 6 to 8 nm.

[0009] Furthermore, the separation method is centrifugation or vacuum filtration; the washing solvent is at least one of deionized water, anhydrous ethanol and acetone, and the product is washed with the washing solvent until the product pH is neutral; the drying method is at least one of forced air drying, natural air drying, freeze drying and vacuum drying.

[0010] Secondly, the present invention provides anatase titanium dioxide nanosheets with exposed {001} crystal planes, which are prepared by the above-described method for preparing anatase titanium dioxide nanosheets with exposed {001} crystal planes.

[0011] Thirdly, the present invention provides an application of anatase titanium dioxide nanosheets with exposed {001} crystal planes prepared by the above-described method in magnesium-based battery cathode materials.

[0012] The beneficial effects of this invention are as follows: This invention uses hydrofluoric acid as a structure control agent for titanium dioxide nanosheets, and prepares anatase titanium dioxide nanosheets with exposed {001} crystal faces through a hydrothermal synthesis method. The obtained anatase titanium dioxide nanosheets have high purity, large specific surface area, and high surface energy, and can be used as positive electrode materials for magnesium-ion batteries and magnesium-lithium hybrid batteries. The preparation method is simple, reproducible, easy to operate, and has the potential for large-scale industrial production. Attached Figure Description

[0013] Figure 1 A flowchart illustrating the preparation method of anatase titanium dioxide nanosheets with exposed {001} crystal planes provided in this embodiment of the invention.

[0014] Figure 2 This is a SEM image of anatase titanium dioxide nanosheets with exposed {001} crystal planes prepared in Example 1 of the present invention.

[0015] Figure 3 SEM image of the cathode material prepared for comparison; Figure 4 The image shows the XRD pattern of anatase titanium dioxide nanosheets with exposed {001} crystal planes prepared in Example 1 of this invention.

[0016] Figure 5 The charge-discharge curves of the anatase titanium dioxide nanosheets with exposed {001} crystal faces prepared in Example 1 of the present invention, after being assembled into a rechargeable magnesium battery, are shown in APC+LiCl electrolyte.

[0017] Figure 6 The charge-discharge curves of the anatase titanium dioxide nanosheets with exposed {001} crystal faces prepared in Example 1 of the present invention, after being assembled into a rechargeable magnesium battery, are shown in APC electrolyte.

[0018] Figure 7 The cyclic voltammetry curves of anatase titanium dioxide nanosheets with exposed {001} crystal planes prepared in Example 1 of the present invention, after being assembled into a rechargeable magnesium battery, are obtained under APC electrolyte.

[0019] Figure 8 The cycling curve of the anatase titanium dioxide nanosheets with exposed {001} crystal faces obtained in Example 1 of the present invention after being assembled into a rechargeable magnesium battery in APC electrolyte. Detailed Implementation

[0020] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0021] In one embodiment, see Figure 1 As shown, the present invention provides a method for preparing anatase titanium dioxide nanosheets with exposed {001} crystal faces. The method includes: adding a titanium source to a hydrofluoric acid solution and mixing and stirring to obtain a reaction precursor; transferring the reaction precursor to a reaction vessel for hydrothermal reaction; after the reaction is completed, cooling, separating, washing and drying to obtain anatase titanium dioxide nanosheets with exposed {001} crystal faces.

[0022] This invention successfully prepared anatase titanium dioxide nanosheets with exposed {001} crystal faces via a hydrothermal synthesis reaction using hydrofluoric acid solution. By exposing the crystal face with the highest surface energy of titanium dioxide, the larger specific surface area provides the material with more magnesium ion adsorption sites and broad ion diffusion channels, thereby reducing the diffusion barrier of magnesium ions in the structure, promoting magnesium ion storage, and improving battery capacity. The obtained anatase titanium dioxide nanosheets with exposed {001} crystal faces exhibit high specific capacity, low diffusion barrier, and high stability. At 500 mAg... -1After 1000 cycles under current, the specific capacity can still be maintained above 75%.

[0023] In a preferred embodiment, 3 to 6 mL of a titanium source is added to every 0.3 to 1.6 mL of a hydrofluoric acid solution with a concentration of ~47%; the titanium source includes tetrabutyl titanate, titanium tetrachloride, or isopropyl titanate.

[0024] After the addition of a titanium source, titanium ions in the reaction system coordinate with fluoride ions to form stable complexes. These complexes gradually transform into titanium dioxide nanosheets during the hydrothermal reaction. By adjusting the concentration of the hydrofluoric acid solution, the amount of titanium source added, and the hydrothermal reaction conditions (such as temperature and time), precise control over the morphology, size, and crystal structure of the product can be achieved.

[0025] In a preferred embodiment, the hydrothermal reaction temperature is 100~220°C and the hydrothermal reaction time is 16~24 hours.

[0026] At lower hydrothermal reaction temperatures, the crystal growth rate is slow, which may result in low crystallinity or uneven morphology of the product. Conversely, at excessively high hydrothermal reaction temperatures, although the crystal growth rate increases, unnecessary side reactions such as crystal agglomeration or phase transformation may occur, thus affecting the product's properties. Therefore, the hydrothermal reaction temperature is set at 100–220 °C.

[0027] Similarly, the choice of reaction time is based on the optimization of the crystal growth process. A shorter hydrothermal reaction time may not be sufficient to completely convert the titanium source into titanium dioxide nanosheets, or may result in incomplete product morphology. On the other hand, an excessively long hydrothermal reaction time may increase energy consumption and cost, and may even lead to overgrowth of crystals and performance degradation. Therefore, the hydrothermal reaction time is set to 16–24 hours.

[0028] By precisely controlling the temperature and time of the hydrothermal reaction, the hydrolysis and condensation reactions of the titanium source can be further promoted, which is beneficial for the formation of anatase titanium dioxide nanosheets with exposed {001} crystal planes. At the same time, the specific constraints of the hydrothermal reaction conditions also help to improve the crystallinity, purity, and stability of the product, thereby enabling it to exhibit superior performance in practical applications.

[0029] In a preferred embodiment, the thickness of the obtained anatase titanium dioxide nanosheets with exposed {001} crystal planes ranges from 6 to 8 nm.

[0030] First, the thinner nanosheet structure implies a larger specific surface area, which facilitates the provision of more active sites and enhances its performance as an electrode active material. Simultaneously, the thin nanosheets also facilitate charge transport and separation, further improving its electrical properties.

[0031] Secondly, the {001} crystal plane is one of the most active crystal planes in anatase titanium dioxide, possessing higher surface energy and stronger adsorption capacity. Therefore, exposing this crystal plane significantly enhances the activity and selectivity of titanium dioxide nanosheets in the reaction.

[0032] Furthermore, nanosheets with a thickness of 6–8 nm exhibit good stability and dispersibility. This helps maintain their excellent performance in practical applications and avoids phenomena such as aggregation or precipitation.

[0033] To obtain nanosheets within this thickness range, precise control of the hydrothermal reaction conditions is required. In addition to the previously mentioned temperature and time ranges, factors such as the concentration of the titanium source, the amount of hydrofluoric acid used, the pH of the reaction solution, and post-reaction processing must also be considered. By comprehensively considering these factors, precise control of the nanosheet thickness can be achieved.

[0034] In a preferred embodiment, the separation method is centrifugation or vacuum filtration. The washing solvent is at least one selected from deionized water, anhydrous ethanol, and acetone, and the product is washed with the washing solvent until the product pH is neutral. The drying method is at least one selected from forced-air drying, natural air drying, freeze drying, and vacuum drying.

[0035] First, in the separation step, two methods were employed: centrifugation and vacuum filtration. Centrifugation uses centrifugal force to separate the reaction products from the solution, suitable for processing large quantities of products and enabling rapid separation. Vacuum filtration uses negative pressure to form a filter cake on filter paper, thus separating the reaction products from the solution; this method is suitable for processing products with high viscosity or fine particles. Both methods effectively separate titanium dioxide nanosheets from the reaction solution, facilitating subsequent processing.

[0036] Secondly, in the washing step, at least one of deionized water, anhydrous ethanol, and acetone was selected as the washing solvent. These solvents all have good solubility and volatility, effectively removing residues and impurities from the product surface. Multiple washes until the product's pH is neutral ensure its purity and stability. Careful control of the number of washes and washing time is necessary during the washing process to avoid unnecessary loss or damage to the product.

[0037] Finally, in the drying step, several drying methods are provided for selection, including at least one of the following: forced-air drying, natural air drying, freeze drying, and vacuum drying. Forced-air drying uses hot air to rapidly evaporate moisture or solvents from the product, suitable for processing large quantities of product and situations where drying time is critical. Natural air drying involves placing the product in a well-ventilated environment to air dry naturally, suitable for situations where drying time is not critical and production volume is small. Freeze drying involves freezing the product at low temperatures and then removing moisture through sublimation under reduced pressure, suitable for processing volatile or heat-sensitive products. Vacuum drying involves heating and drying the product under vacuum conditions, which accelerates the drying process and reduces the product's contact time with oxygen, thereby protecting the product's properties.

[0038] In summary, by selecting appropriate separation, washing, and drying methods, the prepared anatase titanium dioxide nanosheets with exposed {001} crystal faces can be effectively post-processed to ensure their purity and stability, providing high-quality samples for subsequent characterization and applications.

[0039] In one embodiment, the present invention also provides anatase titanium dioxide nanosheets with exposed {001} crystal planes, which are prepared by the above-described method for preparing anatase titanium dioxide nanosheets with exposed {001} crystal planes.

[0040] In one embodiment, the present invention also provides the application of anatase titanium dioxide nanosheets with exposed {001} crystal planes prepared by the above-described method in magnesium-based battery cathode materials.

[0041] Furthermore, the present invention also provides a method for preparing a positive electrode sheet, comprising the following steps: 1) Using the prepared anatase titanium dioxide nanosheets with exposed {001} crystal faces as the positive electrode active material, the positive electrode active material was ground and then uniformly mixed with a binder and a conductive agent at a mass ratio of 7:2:1 to obtain a mixture. Then the mixture was added to NMP (N-methylpyrrolidone) and stirred for 8~12 h to obtain a positive electrode material slurry.

[0042] 2) Coat the positive electrode material slurry onto carbon paper or molybdenum foil, and place it in a vacuum oven to dry at 80~100℃ for 10~12 hours to obtain the positive electrode sheet. Finally, cut the positive electrode sheet into round pieces with a diameter of 10mm and place them in a glove box for later use.

[0043] In the assembly of a magnesium-based battery, the positive electrode is prepared using anatase titanium dioxide nanosheets with exposed {001} crystal faces, obtained by the preparation method described in this invention, as the positive electrode active material. The negative electrode uses magnesium foil with a purity of 99.9% or 99.99%. The magnesium foil needs to be surface-polished before use. It is polished with sandpaper of 1200 molybdenum or higher until the surface is smooth and free of scratches. Then, it is ultrasonically cleaned in anhydrous alcohol and finally dried in a vacuum oven to obtain the negative electrode.

[0044] The electrolyte is selected appropriately according to the type of assembled battery. For example, when the assembled battery is a magnesium-ion battery, the electrolyte is commercially available APC electrolyte. When the assembled battery is a magnesium-lithium hybrid battery, the electrolyte is a 0.4 M LiCl + 0.4 M APC mixed electrolyte, prepared as follows: Weigh 0.2~1 gram of lithium chloride (LiCl) and add it to 10~20 ml of commercial APC electrolyte, stir for at least 10 hours to obtain the mixed electrolyte.

[0045] It should be noted that, in addition to the positive electrode, negative electrode, and electrolyte, the battery also consists of a separator and a current collector. The separator is a glass fiber separator, which is known in the art, while the current collector is a non-corrosive material such as carbon paper. The battery assembly and electrolyte preparation are carried out in an argon-filled glove box, with water and oxygen content maintained below 0.01 ppm.

[0046] The following will illustrate this with specific examples.

[0047] Example 1: A method for preparing anatase titanium dioxide nanosheets with exposed {001} crystal planes, the method comprising the following steps: S1, 5 mL of tetrabutyl titanate solution was added to 0.6 mL of 47% hydrofluoric acid solution and stirred for 1 hour to obtain the reaction precursor.

[0048] S2, the reaction precursor is transferred to the reactor for hydrothermal reaction at a temperature of 180°C for 12 hours.

[0049] S3. After the reaction is complete, the anatase titanium dioxide nanosheets with exposed {001} crystal faces are obtained by cooling, separation, washing and drying.

[0050] The separation method is centrifugation, with 3-6 centrifugations. The product is washed with deionized water / anhydrous ethanol / acetone using the washing solvents until its pH is neutral. Initial drying to remove moisture is achieved by forced-air drying for 1-3 hours, followed by further drying under vacuum at 80-100°C for 12-18 hours.

[0051] Comparative Example: A method for preparing anatase titanium dioxide nanosheets with exposed {001} crystal planes is provided. The main steps are the same as in the above examples, except that the titanium source is different. Specifically, 5 mL of isopropyl titanate is added to 0.6 mL of a 47% hydrofluoric acid solution and stirred to obtain a reaction precursor; the reaction precursor is then transferred to a reaction vessel for hydrothermal reaction.

[0052] The obtained product was analyzed by SEM, and the results are shown in [reference needed]. Figure 2 The results indicate that the prepared product has a regular morphology, exhibits a nanosheet structure with a rectangular outline (side length of 40~60 nm), and a large specific surface area.

[0053] Products obtained by comparison, such as Figure 3 As shown, the obtained product is a large bulk polyhedral crystal with a smaller specific surface area than the product obtained in Example 1.

[0054] XRD analysis was performed on the product obtained in Example 1, and the results are shown in [reference needed]. Figure 4 The obtained structure is a complete, smooth, and uniform sheet-like anatase titanium dioxide with exposed {001} crystal planes. The main peak clearly corresponds to the standard card, and there are no impurity peaks.

[0055] To verify the performance of the product obtained in Example 1, an anatase titanium dioxide nanosheets with exposed {001} crystal faces obtained in Example 1 were used as the positive electrode active material to prepare a positive electrode sheet, followed by magnesium-based battery assembly. The specific steps for assembling the magnesium-based battery are as follows: 1) Using the prepared anatase titanium dioxide nanosheets with exposed {001} crystal faces as the positive electrode active material, the positive electrode active material was ground and then uniformly mixed with a binder and a conductive agent at a mass ratio of 7:2:1 to obtain a mixture. Then the mixture was added to NMP (N-methylpyrrolidone) and stirred for 12 h to obtain a positive electrode material slurry.

[0056] 2) Coat the positive electrode material slurry onto carbon paper or molybdenum foil, and place it in a vacuum oven to dry at 100°C for 12 hours to obtain the positive electrode sheet. Finally, cut the positive electrode sheet into round pieces with a diameter of 10mm and place them in a glove box for later use.

[0057] 3) Preparation of electrolytes: Two types of electrolytes are used: a magnesium ion electrolyte and a magnesium-lithium dual-salt mixed electrolyte. The magnesium ion electrolyte is a commercially available APC electrolyte. The magnesium-lithium mixed electrolyte is prepared by adding 0.4 M LiCl + 0.4 M APC electrolyte. The preparation method is as follows: Weigh 0.2 g of lithium chloride (LiCl) and add it to 10 mL of commercial APC electrolyte. Stir for at least 10 hours to obtain the mixed electrolyte.

[0058] 4) Prepare the negative electrode sheet: Use 1200-grit sandpaper to polish a 0.1mm thick, 11mm diameter magnesium foil disc until it is smooth and free of scratches. Then, ultrasonically clean it in anhydrous ethanol. Next, place it in a vacuum oven and dry it at 60℃ for 12 hours. Finally, transfer it to a glove box for later use.

[0059] 5) Using a battery casing, the separator, the positive electrode, the negative electrode prepared by the above method, and the electrolyte are assembled in a conventional manner to obtain a magnesium-based battery.

[0060] The electrochemical performance of the obtained magnesium-based battery was tested, and the results are shown in [reference needed]. Figures 5 to 7 .

[0061] Depend on Figure 5 It can be seen that the cathode material prepared in Example 1 has a specific capacity as high as 280 mAh / g in the dual-salt electrolyte and exhibits a clear charge-discharge plateau. The current density used in the test was 50 mA / g.

[0062] Depend on Figure 6 It can be seen that the cathode material prepared in Example 1 has a specific capacity of 67 mAh / g in pure magnesium electrolyte under low current.

[0063] Depend on Figure 7 It can be seen that the CV curve of the positive electrode material prepared in Example 1 was tested at a voltage of 0.1 mV. Figure 6 It can be seen that there are relatively obvious redox peaks in pure magnesium electrolyte.

[0064] Depend on Figure 8 It can be seen that the cycling curve of the positive electrode material prepared in Example 1 was tested using a current density of 200 mA / g. Figure 8 It can be seen that after 20 cycles, the specific capacity can still be maintained at over 85%.

Claims

1. A magnesium-based battery, characterized in that: Includes positive electrode, negative electrode, electrolyte, separator, and current collector; The preparation of the positive electrode includes: A titanium source was added to a hydrofluoric acid solution and mixed with stirring to obtain a reaction precursor. 3-6 mL of titanium source was added to every 0.3-1.6 mL of a 47% hydrofluoric acid solution. The titanium source included tetrabutyl titanate, titanium tetrachloride, or isopropyl titanate. The reaction precursor was transferred to a reaction vessel for hydrothermal reaction at a temperature of 100-220°C for 16-24 hours. After the reaction, the precursor was cooled, separated, washed, and dried to obtain anatase titanium dioxide nanosheets with an exposed {001} crystal plane and a thickness ranging from 6-8 nm. Using the anatase titanium dioxide nanosheets with exposed {001} crystal faces as the positive electrode active material, the positive electrode active material was ground and then uniformly mixed with binder and conductive agent at a mass ratio of 7:2:1 to obtain a mixture. Then the mixture was added to N-methylpyrrolidone and stirred for 8~12h to obtain a positive electrode material slurry. The positive electrode material slurry is coated onto the current collector and placed in a vacuum oven to dry at 80~100℃ for 10~12 hours to obtain the positive electrode sheet; The negative electrode uses magnesium foil; The electrolyte is selected appropriately according to the type of assembled battery. When the assembled battery is a magnesium-ion battery, the electrolyte is APC electrolyte; when the assembled battery is a magnesium-lithium hybrid battery, the electrolyte is a mixture of 0.4M LiCl and 0.4M APC electrolyte. The preparation method is as follows: weigh 0.2~1 gram of LiCl and add it to 10~20 ml of APC electrolyte, stir for 10 hours or more to obtain the mixed electrolyte.

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