A single-crystal NaTi2(PO4)3 with a micron-sized cubic structure, its preparation method and applications

Abstract

The application relates to the technical field of aqueous sodium-ion batteries, and particularly relates to a single-crystal NaTi2(PO4)3 with a micro-cubic structure as well as a preparation method and application thereof. x The single-crystal NaTi2(PO4)3 is prepared from a Mxene matrix and has a micro-cubic structure and unique single-crystal characteristics. The preparation method of the NaTi2(PO4)3 is simple and easy to operate, and is favorable for large-scale preparation. The single-crystal NaTi2(PO4)3 prepared by the application has a micro-cubic structure, and the structural characteristics are favorable for rapid transmission of electrons. The micro-cubic structure is uniform in size, is favorable for increasing the contact area of electrolyte and electrode material, and simultaneously provides more active sites. The micro-morphology of the micro-cubic structure and the unique single-crystal structure make the NaTi2(PO4)3 have obvious advantages when used as a negative electrode material of an aqueous sodium-ion battery, and significantly improve the energy density and cycle life of the aqueous sodium-ion battery.

Description

Technical Field

[0001] This invention relates to the field of aqueous sodium-ion battery technology, specifically to a single-crystal NaTi2(PO4)3 with a micron-sized cubic structure, its preparation method, and its applications. Background Technology

[0002] The information disclosed in this background section is intended to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In recent years, the increasing demand for traditional energy and the severe environmental problems have made the pursuit of efficient, low-cost, safe, green, and pollution-free electrochemical energy storage devices more urgent. Aqueous sodium-ion batteries have become a promising new energy source due to their lower cost, higher safety, better sustainability, and suitability for large-scale energy storage needs. However, due to the limitations of water's poor stability and the occurrence of side reactions such as hydrogen evolution and oxygen evolution, the selection and performance optimization of electrode materials are particularly important for the development of aqueous sodium-ion batteries.

[0004] NASICON-type NaTi2(PO4)3 possesses a unique three-dimensional (3D) open framework structure, exhibiting excellent chemical stability and Na... + Fast transmission, suitable voltage platform (~-0.85V vs. SCE) and large theoretical capacity (~133mAh g) -1 These excellent properties make NaTi2(PO4)3 stand out from many candidate anode materials. Unfortunately, the inherently low electronic conductivity of NaTi2(PO4)3 leads to poor coulombic rate and long-term cycling behavior, limiting its practical application in aqueous sodium-ion batteries. Therefore, it is very meaningful to optimize the electrochemical performance of NaTi2(PO4)3 by rationally designing its microstructure, improving its structure, and enhancing its electronic conductivity and structural stability. However, most current synthesis methods for NaTi2(PO4)3 are cumbersome, require high synthesis conditions, have low yields, and cannot be prepared on a large scale. At the same time, their microstructure and structural performance are poor, resulting in little improvement in performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a single-crystal NaTi2(PO4)3 with a micron-sized cubic structure, its preparation method, and its applications. Compared to existing NaTi2(PO4)3, the method and applications provided by this invention utilize Ti3C2T... x Mxene-derived single-crystal NaTi2(PO4)3 with a micron-sized cubic structure exhibits superior electrochemical performance. To achieve the above objectives, this invention discloses the following technical solution:

[0006] In a first aspect of the invention, a single-crystal NaTi2(PO4)3 is provided, wherein the single-crystal NaTi2(PO4)3 is formed by using a few-layer Ti3C2T x Mxene is used as a matrix and is derived from it to prepare micron-cubic structures with unique single-crystal properties; the side length of the micron-cubic structure is 0.2 to 5.0 micrometers.

[0007] Furthermore, the lattice fringes of the single-crystal NaTi2(PO4)3 are regular and distinct, and the diffraction spots show a typical regular point arrangement. This demonstrates that the single-crystal NaTi2(PO4)3 provided by this invention has obvious single-crystal characteristics, and its unique single-crystal structure is conducive to the rapid transport of electrons in electrochemical processes.

[0008] Furthermore, the single-crystal NaTi2(PO4)3 exhibits a uniform and regular cubic structure with a large specific surface area. The stacked cubes form abundant porous structures, significantly increasing the number of electroactive sites and enhancing ion transport rates. The uniform micron-sized cubes and large specific surface area increase the effective contact area between the electrode material and the electrolyte, resulting in excellent electrochemical performance of NaTi2(PO4)3 in electrochemical reactions.

[0009] In a second aspect of the present invention, a method for preparing the above-mentioned single-crystal NaTi2(PO4)3 is provided, comprising the following steps:

[0010] (1) Few layers of Ti3C2T x MXene, sodium source, and phosphorus source are mixed and stirred until homogeneous to obtain a mixed solution;

[0011] (2) The mixed solution in step (1) is subjected to hydrothermal reaction; after the reaction is complete, it is cooled to room temperature, washed, centrifuged to collect the lower solid product, and the product is dried to obtain single crystal NaTi2(PO4)3 with micron cubic structure.

[0012] Further, in step (1), the Ti3C2T x Mxene is a few-layer Ti3C2T x MXene, with the number of layers controlled between 2 and 3.

[0013] Furthermore, in step (1), the sodium source and the few-layer Ti3C2T x The molar ratio of MXene to phosphorus source is 1:2:2-4. Among them, sodium source and few-layer Ti3C2T... x When the molar ratio of MXene to phosphorus source is 1:2:3, the prepared single-crystal NaTi2(PO4)3 has higher purity and better performance.

[0014] Further, in step (1), the sodium source is at least one of sodium dihydrogen phosphate dihydrate, anhydrous sodium acetate, sodium carbonate, and disodium bicarbonate.

[0015] Further, in step (1), the phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0016] Furthermore, in step (2), the solvothermal reaction temperature is preferably controlled between 120 and 180°C, and the time is preferably controlled between 3 and 10 hours. The temperature and time of the solvothermal reaction have a significant impact on the microstructure and size of single-crystal NaTi2(PO4)3.

[0017] In a third aspect, the invention provides the application of the aforementioned single-crystal NaTi2(PO4)3 with a micron-sized cubic structure in energy storage devices, preferably as a negative electrode material for aqueous sodium-ion batteries. Using the single-crystal NaTi2(PO4)3 provided by this invention as a negative electrode material can effectively alleviate the problems of instability, material dissolution, and capacity decay existing in current negative electrode materials in aqueous batteries, which is of great significance for constructing batteries with high safety, long lifespan, and high energy density.

[0018] Compared with the prior art, the present invention has the following beneficial and unique effects:

[0019] (1) Currently, with Ti3C2T x The preparation method of single-crystal NaTi2(PO4)3 with a micron-cubic structure derived from Mxene, as well as its application in aqueous sodium-ion batteries, have not yet been reported. (Ti3C2T) x Mxene has an excellent structure and is non-toxic and harmless. This invention uses few-layer Ti3C2T x Using Mxene as the titanium source, single-crystal NaTi2(PO4)3 with a micron-sized cubic structure was prepared. (Few-layer Ti3C2T) x The introduction of Mxene not only solves the problem of limiting reaction conditions in the synthesis of electrode materials by other titanium sources, but also reduces the number of impurity atoms in the electrode materials, enabling NaTi2(PO4)3 to be synthesized effectively and improving the preparation efficiency.

[0020] (2) The single-crystal NaTi2(PO4)3 with a micron cubic structure provided by the present invention has unique single-crystal characteristics that greatly increase the electron transport rate and significantly improve the energy density and cycle life of aqueous sodium-ion batteries.

[0021] (3) The single-crystal NaTi2(PO4)3 with a micron-cubic structure provided by this invention is composed of a large number of micron-cubic stacks, the side length of which is between 0.2 and 5.0 micrometers and the size is uniform. The unique and uniform cubic morphology and large specific surface area can significantly increase the electrochemical reaction active sites. There are pores between the micron-cubic stacks, which have obvious mesoporous characteristics and are beneficial to improving the electron and ion transport efficiency of NaTi2(PO4)3.

[0022] (4) The single-crystal NaTi2(PO4)3 with a micron cubic structure provided by the present invention is composed of few-layer Ti3C2T x Mxene, sodium source, and phosphorus source are obtained through a simple hydrothermal reaction. The preparation method is simple, easy to control, and conducive to the large-scale preparation of electrode materials. Attached Figure Description

[0023] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings, wherein:

[0024] Figure 1 The X-ray diffraction (XRD) patterns of single-crystal NaTi2(PO4)3 with a micron-sized cubic structure obtained in the first, second, and third embodiments of the present invention are shown.

[0025] Figure 2 This is a scanning electron microscope (SEM) image of the single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the first embodiment.

[0026] Figure 3 This is a scanning electron microscope (SEM) image of the single-crystal NaTi2(PO4)3 with a micron-sized cubic structure obtained in the second embodiment.

[0027] Figure 4 This is a scanning electron microscope (SEM) image of the single-crystal NaTi2(PO4)3 with a micron-sized cubic structure obtained in the third embodiment.

[0028] Figure 5 This is a SAED (Sequencing Analysis of the Diffusion Spots) pattern of a single-crystal NaTi2(PO4)3 with a micron-sized cubic structure obtained in the second embodiment.

[0029] Figure 6 X-ray diffraction (XRD) pattern of NaTi2(PO4)3 prepared for comparison.

[0030] Figure 7 The image shows a scanning electron microscope (SEM) image of NaTi2(PO4)3 prepared in comparison.

[0031] Figure 8 Cyclic voltammetry (CV) diagrams of single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared according to the first, second, and third embodiments are shown.

[0032] Figure 9 Cyclic voltammetry (CV) plot of NaTi2(PO4)3 prepared for comparison

[0033] Figure 10 The graph shows a comparison of the cycle performance of NaTi2(PO4)3 prepared in the second embodiment and Comparative Example 1 as the negative electrode of an aqueous sodium-ion battery. Specific Implementation

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods or product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only. The invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0036] First Embodiment

[0037] A method for preparing single-crystal NaTi2(PO4)3 with a micron-sized cubic structure includes the following steps:

[0038] (1) Multilayer Ti3C2T x Preparation of Mxene: 2g of lithium fluoride (LiF) and 9M hydrochloric acid (HCl) were stirred in a 100mL polytetrafluoroethylene beaker for 30min (400rpm). After thorough mixing, 2g of MAX-Ti3AlC2 (the reaction is vigorous and must be carried out in a fume hood) was slowly added to the above solution. After stirring for 30min, the mixture was transferred to a heated magnetic stirrer, and the reaction temperature was adjusted to 35℃. Stirring was continued for 24 hours. After the reaction was complete, the obtained reaction liquid was centrifuged and washed repeatedly with deionized water until the pH reached 6. The lower solid precipitate was collected for later use.

[0039] (2) Few-layered Ti3C2T xMxene preparation: Add ethanol to the precipitate collected in step (1) and sonicate for 1 hour, then centrifuge (10000 rpm, 10 minutes) and discard the supernatant. Add 20 ml of deionized water to the separated solid product and centrifuge at 3500 rpm for 3 minutes. Collect the dark brown supernatant as a fractional dispersion. Repeat this step to obtain more fractional dispersions for later use.

[0040] (3) Take 0.04g of the few-layer Ti3C2T from step (2). x The dispersion of MXene was placed in the liner of a 100 mL reactor. Subsequently, 10 mL of a solution containing 2.48 g of sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O) and 1.5 mL of phosphoric acid (H3PO4) were added. After stirring continuously at room temperature for half an hour, a homogeneous mixed solution was obtained for later use.

[0041] (4) The liner containing the mixture in step (3) is placed into the reactor and heated to 160°C for 4 hours. After naturally cooling to room temperature, it is washed with deionized water and ethanol, and the lower solid product is collected by centrifugation. It is then dried in a vacuum drying oven at 60°C to obtain single-crystal NaTi2(PO4)3 cubic material.

[0042] Second Embodiment

[0043] A method for preparing single-crystal NaTi2(PO4)3 with a micron-sized cubic structure includes the following steps:

[0044] (1) Multilayer Ti3C2T x Preparation of Mxene: 2g of lithium fluoride (LiF) and 9M hydrochloric acid (HCl) were stirred in a 100mL polytetrafluoroethylene beaker for 30min (400rpm). After thorough mixing, 2g of MAX-Ti3AlC2 (the reaction is vigorous and must be carried out in a fume hood) was slowly added to the above solution. After stirring for 30min, the mixture was transferred to a heated magnetic stirrer, and the reaction temperature was adjusted to 35℃. Stirring was continued for 24 hours. After the reaction was complete, the obtained reaction liquid was centrifuged and washed repeatedly with deionized water until the pH reached 6. The lower solid precipitate was collected for later use.

[0045] (2) Few-layered Ti3C2T x Mxene preparation: Add ethanol to the precipitate collected in step (1) and sonicate for 1 hour, then centrifuge (10000 rpm, 10 minutes) and discard the supernatant. Add 20 ml of deionized water to the separated solid product and centrifuge at 3500 rpm for 3 minutes. Collect the dark brown supernatant as a fractional dispersion. Repeat this step to obtain more fractional dispersions for later use.

[0046] (3) Take 0.04g of the few-layer Ti3C2T from step (2). x The dispersion of MXene was placed in the liner of a 100 mL reactor. Subsequently, 10 mL of a solution containing 2.48 g of sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O) and 1.5 mL of phosphoric acid (H3PO4) were added. After stirring continuously at room temperature for half an hour, a homogeneous mixed solution was obtained for later use.

[0047] (4) The liner containing the mixture in step (3) is placed into the reactor and heated to 160°C and kept at that temperature for 6 hours. After naturally cooling to room temperature, it is washed with deionized water and ethanol, and the lower solid product is collected by centrifugation. It is then dried in a vacuum drying oven at 60°C to obtain single-crystal NaTi2(PO4)3 cubic material.

[0048] Third Embodiment

[0049] A method for preparing single-crystal NaTi2(PO4)3 with a micron-sized cubic structure includes the following steps:

[0050] (1) Multilayer Ti3C2T x Preparation of Mxene: 2g of lithium fluoride (LiF) and 9M hydrochloric acid (HCl) were stirred in a 100mL polytetrafluoroethylene beaker for 30min (400rpm). After thorough mixing, 2g of MAX-Ti3AlC2 (the reaction is vigorous and must be carried out in a fume hood) was slowly added to the above solution. After stirring for 30min, the mixture was transferred to a heated magnetic stirrer, and the reaction temperature was adjusted to 35℃. Stirring was continued for 24 hours. After the reaction was complete, the obtained reaction liquid was centrifuged and washed repeatedly with deionized water until the pH reached 6. The lower solid precipitate was collected for later use.

[0051] (2) Few-layered Ti3C2T x Mxene preparation: Add ethanol to the precipitate collected in step (1) and sonicate for 1 hour, then centrifuge (10000 rpm, 10 minutes) and discard the supernatant. Add 20 ml of deionized water to the separated solid product and centrifuge at 3500 rpm for 3 minutes. Collect the dark brown supernatant as a fractional dispersion. Repeat this step to obtain more fractional dispersions for later use.

[0052] (3) Take 0.04g of the few-layer Ti3C2T from step (2). x The dispersion of MXene was placed in the liner of a 100 mL reactor. Subsequently, 10 mL of a solution containing 2.48 g of sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O) and 1.5 mL of phosphoric acid (H3PO4) were added. After stirring continuously at room temperature for half an hour, a homogeneous mixed solution was obtained for later use.

[0053] (4) The liner containing the mixture from step (3) is placed into the reactor and heated to 160°C for 8 hours. After naturally cooling to room temperature, it is washed with deionized water and ethanol, and the lower solid product is collected by centrifugation. It is then dried in a vacuum drying oven at 60°C to obtain single-crystal NaTi2(PO4)3 cubic material.

[0054] Fourth embodiment

[0055] A method for preparing single-crystal NaTi2(PO4)3 with a micron-sized cubic structure includes the following steps:

[0056] (1) Multilayer Ti3C2T x Preparation of Mxene: 2g of lithium fluoride (LiF) and 9M hydrochloric acid (HCl) were stirred in a 100mL polytetrafluoroethylene beaker for 30min (400rpm). After thorough mixing, 2g of MAX-Ti3AlC2 (the reaction is vigorous and must be carried out in a fume hood) was slowly added to the above solution. After stirring for 30min, the mixture was transferred to a heated magnetic stirrer, and the reaction temperature was adjusted to 35℃. Stirring was continued for 24 hours. After the reaction was complete, the obtained reaction liquid was centrifuged and washed repeatedly with deionized water until the pH reached 6. The lower solid precipitate was collected for later use.

[0057] (2) Few-layered Ti3C2T x Mxene preparation: Add ethanol to the precipitate collected in step (1) and sonicate for 1 hour, then centrifuge (10000 rpm, 10 minutes) and discard the supernatant. Add 20 ml of deionized water to the separated solid product and centrifuge at 3500 rpm for 3 minutes. Collect the dark brown supernatant as a fractional dispersion. Repeat this step to obtain more fractional dispersions for later use.

[0058] (3) Take 0.04g of the few-layer Ti3C2T from step (2). x The dispersion of MXene was placed in the liner of a 100 mL reactor. Subsequently, 10 mL of a solution containing 2.48 g of sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O) and 2 mL of phosphoric acid (H3PO4) were added. After stirring continuously at room temperature for half an hour, a homogeneous mixed solution was obtained for later use.

[0059] (4) The liner containing the mixture in step (3) is placed into the reactor and heated to 140°C and kept at that temperature for 6 hours. After naturally cooling to room temperature, it is washed with deionized water and ethanol, and the lower solid product is collected by centrifugation. It is then dried in a vacuum drying oven at 60°C to obtain single-crystal NaTi2(PO4)3 cubic material.

[0060] Fifth embodiment

[0061] A method for preparing single-crystal NaTi2(PO4)3 with a micron-sized cubic structure includes the following steps:

[0062] (1) Multilayer Ti3C2T x Preparation of Mxene: 2g of lithium fluoride (LiF) and 9M hydrochloric acid (HCl) were stirred in a 100mL polytetrafluoroethylene beaker for 30min (400rpm). After thorough mixing, 2g of MAX-Ti3AlC2 (the reaction is vigorous and must be carried out in a fume hood) was slowly added to the above solution. After stirring for 30min, the mixture was transferred to a heated magnetic stirrer, and the reaction temperature was adjusted to 35℃. Stirring was continued for 24 hours. After the reaction was complete, the obtained reaction liquid was centrifuged and washed repeatedly with deionized water until the pH reached 6. The lower solid precipitate was collected for later use.

[0063] (2) Few-layered Ti3C2T x Mxene preparation: Add ethanol to the precipitate collected in step (1) and sonicate for 1 hour, then centrifuge (10000 rpm, 10 minutes) and discard the supernatant. Add 20 ml of deionized water to the separated solid product and centrifuge at 3500 rpm for 3 minutes. Collect the dark brown supernatant as a fractional dispersion. Repeat this step to obtain more fractional dispersions for later use.

[0064] (3) Take 0.04g of the few-layer Ti3C2T from step (2). x The dispersion of MXene was placed in the liner of a 100 mL reactor. Subsequently, 10 mL of a solution containing 1.3 g of anhydrous sodium acetate (CH3COONa) and 1.5 mL of phosphoric acid (H3PO4) were added. After stirring continuously at room temperature for half an hour, a homogeneous mixed solution was obtained and set aside for later use.

[0065] (4) The liner containing the mixture in step (3) is placed into the reactor and heated to 160°C and kept at that temperature for 6 hours. After naturally cooling to room temperature, it is washed with deionized water and ethanol, and the lower solid product is collected by centrifugation. It is then dried in a vacuum drying oven at 60°C to obtain single-crystal NaTi2(PO4)3 cubic material.

[0066] Comparative Example 1

[0067] A method for preparing NaTi2(PO4)3 includes the following steps:

[0068] (1) Dissolve 3.4 ml of tetrabutyl titanate in 10 ml of ethanol, then add 10 ml of a solution containing 0.83 g of sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O) and 0.5 mL of phosphoric acid (H3PO4). Stir continuously at room temperature for half an hour to obtain a homogeneous mixed solution for later use.

[0069] (2) The liner containing the mixture in step (1) is placed into the reactor and heated to 160°C and kept at that temperature for 6 hours. After naturally cooling to room temperature, it is washed with deionized water and ethanol, and the lower solid product is collected by centrifugation. It is then dried in a vacuum drying oven at 60°C to obtain NaTi2(PO4)3 material.

[0070] Performance testing

[0071] Figure 1 The XRD patterns of single-crystal NaTi2(PO4)3 with a micron-sized cubic structure obtained in the first, second, and third embodiments are shown in the standard card, indicating that we have successfully synthesized the NaTi2(PO4)3 phase.

[0072] Figure 2 The image shows a SEM image of a single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the first embodiment. It can be seen that the single-crystal NaTi2(PO4)3 prepared in this embodiment is relatively small, with a side length of 0.3 to 0.8 micrometers.

[0073] Figure 3 The image shows a SEM image of a single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the second embodiment. It can be seen that the single-crystal NaTi2(PO4)3 prepared in this embodiment has a complete structure, uniform size, good morphology, and a side length of 0.5 to 1.3 micrometers.

[0074] Figure 4 The image shows a SEM image of a single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the third embodiment. It can be seen that the single-crystal NaTi2(PO4)3 prepared in this embodiment is relatively large, with a side length of 1.2 to 3.5 micrometers.

[0075] Figure 5 The image shows the SAED pattern of single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the second embodiment. It can be seen that the clear and orderly diffraction spots of the single-crystal NaTi2(PO4)3 prepared in this embodiment exhibit a regular parallelogram arrangement. This structure helps to accelerate the transport of electrons and ions.

[0076] Figure 6 The XRD pattern of NaTi2(PO4)3 prepared for comparison.

[0077] Figure 7 The image shown is a SEM image of NaTi2(PO4)3 prepared for comparison; it is not a cubic structure.

[0078] Further comparison of the superior electrochemical performance was conducted. To prepare the working electrode, an active material, acetylene black, and polytetrafluoroethylene (PTFE) in a mass ratio of 8:1:1 were uniformly mixed and then smoothly coated onto a clean nickel foam substrate. The mixture was then vacuum-dried at 110°C for 11 hours. The single-crystal NaTi₂(PO₄)₃ with a micron-sized cubic structure prepared in the first, second, and third examples, as well as the NaTi₂(PO₄)₃ prepared in the comparative example, were used for testing. The electrolyte was a 1M Na₂SO₄ solution. The test results are as follows: Figure 8 and Figure 9 As shown.

[0079] Figure 8 The CV diagrams of single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the first, second, and third embodiments as the negative electrode of an aqueous sodium-ion battery show that all samples have obvious redox peaks, and the single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the second embodiment has a larger peak area.

[0080] Figure 9 The CV curve of NaTi2(PO4)3 prepared as a comparative example as the negative electrode of an aqueous sodium-ion battery shows that the redox peaks are not obvious and there is severe polarization.

[0081] Figure 10 The single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the second embodiment and the NaTi2(PO4)3 prepared in the comparative example were used as anodes in aqueous sodium-ion batteries at 2C (1C = 133 mAh g). -1 The lower loop capacity graph. From Figure 10 As can be seen from the data, the single-crystal NaTi2(PO4)3 prepared in the second embodiment has a first-cycle capacity as high as 78.3 mAh g. -1 The NaTi2(PO4)3 prepared in the comparative example had an initial capacity of only 30.3 mAh g. -1 This demonstrates that the single-crystal NaTi2(PO4)3 with a micron-sized cubic structure prepared in the second embodiment exhibits excellent electrochemical performance. This is attributed to the superior structural characteristics of the single-crystal NaTi2(PO4)3 prepared in the second embodiment.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A single-crystal NaTi2(PO4)3, characterized in that, The single-crystal NaTi2(PO4)3 is composed of few-layer Ti3C2T x The microcube is prepared using Mxene as a matrix and derived from it, and has a microcube structure; the side length of the microcube is 0.2~5.0 micrometers; The method for preparing the single-crystal NaTi2(PO4)3 includes the following steps: (1) Few layers of Ti3C2T x MXene, sodium source, and phosphorus source are mixed and stirred until homogeneous to obtain a mixed solution; the few-layer Ti3C2T x The number of Mxene layers should be controlled between 2 and 3; (2) The mixed solution in step (1) is subjected to hydrothermal reaction; after the reaction is complete, it is cooled to room temperature, washed, centrifuged to collect the lower solid product, and the product is dried to obtain single crystal NaTi2(PO4)3 with micron cubic structure.

2. The single-crystal NaTi2(PO4)3 according to claim 1, characterized in that, In step (1), the sodium source and the few-layer Ti3C2T x The molar ratio of MXene to phosphorus source is 1:2:2~4.

3. The single-crystal NaTi2(PO4)3 according to claim 2, characterized in that, The sodium source and few-layer Ti3C2T x The molar ratio of MXene to phosphorus source is 1:2:

3.

4. The single-crystal NaTi2(PO4)3 according to claim 1, characterized in that, In step (1), the sodium source is at least one of sodium dihydrogen phosphate dihydrate, anhydrous sodium acetate, sodium carbonate, and sodium bicarbonate; in step (1), the phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

5. The single-crystal NaTi2(PO4)3 according to claim 1, characterized in that, In step (2), the temperature of the hydrothermal reaction is 120~180℃ and the time is controlled at 3~10 hours.

6. The application of single-crystal NaTi2(PO4)3 according to any one of claims 1-5 in energy storage devices.

7. The application of single-crystal NaTi2(PO4)3 in energy storage devices according to claim 6, characterized in that, The application is as a negative electrode material for aqueous sodium-ion batteries.

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