Sodium titanate with layered crystal structure, preparation method of sodium titanate and application of sodium titanate in aqueous magnesium ion battery

Abstract

The invention discloses sodium titanate with a layered crystal structure, a preparation method of the sodium titanate and application of the sodium titanate in a water-based magnesium ion battery, and belongs to the technical field of water-based magnesium ion batteries. According to the invention, the sodium titanate with a layered crystal structure is used as the negative electrode material of the aqueous magnesium ion battery, and due to excellent chemical and structural stability, the sodium titanate can realize reversible Mg < 2 + > intercalation / deintercalation in an aqueous magnesium electrolyte. According to the invention, Na2Ti2O5 and Na2Ti3O7 materials are synthesized by a hydrothermal method and a high-temperature annealing process. In a magnesium chloride electrolyte, the two sodium titanate materials both show extremely low charge and discharge potentials (Na2Ti2O5,-1.3 to-0.6 V vs.SCE; sCE (-1.5 to-1 V vs.SCE) and relatively good cycling stability are achieved. In addition, the charge-discharge specific capacity of the Na2Ti2O5 half cell under the current density of 2A / g is up to 213mAh / g, and the high specific capacity of 150mAh / g is still kept under the high current density of 10A / g. The sodium titanate is an ideal aqueous magnesium battery negative electrode material, has the advantages of low cost and environmental friendliness, and has a great application prospect in the field of aqueous magnesium ion energy storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of aqueous magnesium ion batteries, and particularly relates to a type of sodium titanate with a layered crystal structure, a preparation method thereof, and an application in aqueous magnesium ion batteries. Background Art

[0002] In recent years, multi-valent metal ion (Zn 2+ , Mg 2+ , Ca 2+ , Al 3+ , etc.) aqueous batteries have received extensive attention from researchers due to their advantages such as rich resource reserves, multi-electron transfer characteristics, and inherent safety. Among them, magnesium has more abundant resource reserves (the crustal reserve is ~280 times that of zinc), a lighter relative atomic mass (magnesium: 24.31, zinc: 65.38), and a smaller hydrated ion radius (magnesium: zinc: ), which makes aqueous magnesium ion batteries promising to become the next focus in the research field of low-cost, high-energy / power density batteries. However, the research on aqueous magnesium ion batteries is still in its infancy, especially the development of anode materials lags behind relatively. Among them, the extremely low reduction potential of magnesium metal (-2.37V vs. SHE) makes it prone to intense hydrogen evolution side reactions in water and form an Mg 2+ insulating inert passivation layer, greatly reducing its reversibility and cycle stability. Therefore, aqueous magnesium ion batteries based on magnesium metal anodes are still difficult to meet the actual application requirements in the short term.

[0003] In addition to magnesium metal, currently, a few organic compounds and inorganic vanadium oxides have been reported as anodes in aqueous magnesium ion batteries. However, most organic small molecules and vanadium oxide anodes face serious dissolution problems in aqueous electrolytes. In addition, the limited active sites on the surface of organic molecules make most organic anodes exhibit a low Mg 2+ storage capacity; vanadium-based materials have a specific capacity close to the theoretical value through the continuous redox of multi-valent vanadium at an extremely low current density, while due to reaction kinetics limitations, they also exhibit a low Mg 2+ storage capacity at a higher current density.

[0004] As a low-cost anode, titanium-based materials have the advantages of high theoretical capacity (130 - 350 mAh / g) and low lattice strain, and at the same time show a sufficiently low redox potential (< -1V vs. SHE) in aqueous electrolytes. However, the reaction potential of titanium-based materials is lower than the hydrogen evolution potential of water (-0.41V vs. SHE; pH = 7), and the hydrogen evolution side reaction will still interfere with the reversible insertion and extraction of ions. Especially for magnesium ions with a high ionic potential, some titanium-based materials with a dense structure have Mg 2+High desolvation energy can cause severe electrode polarization and exacerbate side reactions at the solid-liquid interface; completely desolvated bare Mg 2+ The strong interaction with the host lattice may also limit its solid-phase diffusion. Therefore, there has been no research report on the reversible storage of Mg in titanium-based anodes in conventional aqueous electrolytes so far. 2+

[0005] Based on the above reasons, this application is proposed. Summary of the Invention

[0006] Based on the above reasons, aiming at the problems or defects existing in the prior art, the purpose of the present invention is to provide a class of sodium titanates with a layered crystal structure, their preparation methods and applications in aqueous magnesium-ion batteries, to solve or at least partially solve the above technical defects existing in the prior art: The sodium titanate with a layered crystal structure of the present invention exhibits extremely low magnesium ion insertion / extraction potentials (~-1.2V vs. SCE) in a conventional magnesium chloride aqueous solution, has excellent rate performance and cycle stability. Moreover, the sodium titanate with a layered crystal structure of the present invention has an open layer space structure. When used as the anode material of an aqueous magnesium-ion battery, it can reduce the desolvation energy barrier at the solid-liquid interface, promote interfacial charge transfer, and effectively slow down the occurrence of hydrogen evolution side reactions.

[0007] In order to achieve the above first object of the present invention, the technical solution adopted by the present invention is as follows:

[0008] A class of sodium titanates with a layered crystal structure, the molecular formula of the sodium titanate is Na2Ti n O 2n+1 , where: 2 ≤ n ≤ 3, and n is an integer.

[0009] Specifically, in the above technical solution, the sodium titanate with a layered crystal structure is Na2Ti2O5 or Na2Ti3O7.

[0010] Further, in the above technical solution, the Na2Ti2O5 is nanowire-like; the Na2Ti3O7 is a sea urchin-like nanosphere.

[0011] The second object of the present invention is to provide a preparation method of the sodium titanate with the above-mentioned layered crystal structure, which is obtained by hydrothermal reaction of reaction raw materials containing a titanium source and an inorganic sodium salt aqueous solution followed by further high-temperature annealing.

[0012] Specifically, when the sodium titanate with a layered crystal structure is Na2Ti2O5, the preparation method of the Na2Ti2O5 includes the following steps:

[0013] Place a clean and dry titanium substrate into the inner liner of a high-pressure reactor filled with sodium hydroxide solution, seal it, and then heat the sealed reactor to 220 °C for isothermal reaction for 24 hours; after the reaction, take out the titanium substrate, dry it and place it in a tube furnace, and heat it to 450 °C for isothermal annealing for 2 hours under the condition of special gas atmosphere to obtain Na2Ti2O5 film.

[0014] Further, in the preferred embodiment of the present invention, the concentration of the sodium hydroxide solution is 0.5 - 2 mol / L.

[0015] Further, in the above technical solution, the special gas atmosphere consists of hydrogen and argon, for example, it can be composed of 5% (v / v) hydrogen and 95% (v / v) argon.

[0016] Specifically, when the sodium titanate with a layered crystal structure is Na2Ti3O7, the preparation method of Na2Ti3O7 includes the following steps:

[0017] Disperse glycerol evenly in the aqueous solution of titanium source according to the ratio, and then continue to drop the sodium hydroxide solution into the obtained mixed solution according to the ratio to obtain a reaction solution; transfer the reaction solution to the inner liner of a high-pressure reactor, seal it, and then heat the sealed reactor to 200 °C for isothermal reaction for 24 hours; after the reaction, centrifuge the obtained product, collect the precipitate, dry it and place it in a tube furnace, and heat it to 450 °C for isothermal annealing for 2 hours under the condition of special gas atmosphere to obtain Na2Ti3O7 powder.

[0018] Further, in the preferred embodiment of the present invention, the concentration of the aqueous solution of titanium source is 5 - 15 g / L.

[0019] Further, in the preferred embodiment of the present invention, the volume ratio of glycerol to the aqueous solution of titanium source is 1:(1 - 10).

[0020] Further, in the above technical solution, the titanium source is any one of tetrabutyl titanate, butyl titanate, etc.

[0021] Further, in the preferred embodiment of the present invention, the concentration of the sodium hydroxide solution is 5 - 15 mol / L.

[0022] Further, in the preferred embodiment of the present invention, the volume ratio of the aqueous solution of titanium source to the sodium hydroxide solution is (1 - 5):1.

[0023] Further, in the above technical solution, the special gas atmosphere consists of hydrogen and argon, for example, it can be composed of 5% (v / v) hydrogen and 95% (v / v) argon.

[0024] The third object of the present invention is to provide the application of the sodium titanate with the above-mentioned layered crystal structure in an aqueous magnesium ion battery.

[0025] The fourth object of the present invention is to provide a negative electrode material for an aqueous magnesium ion battery. The negative electrode material includes a negative electrode active material, conductive carbon black, and a binder. The negative electrode active material is the Na2Ti3O7 powder described above in the present invention.

[0026] Further, in the above technical solution, the mass ratio of the Na2Ti3O7 powder electrode, conductive carbon black, and binder is 6-8:1-3:1-2.

[0027] Further, in the above technical solution, the conductive carbon black is any one of Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, Super P, etc.

[0028] Further, in the above technical solution, the binder is any one of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), etc.

[0029] The fifth object of the present invention is to provide a negative electrode plate for an aqueous magnesium ion battery. The negative electrode plate includes a current collector and a negative electrode material coated and / or filled on the current collector. Among them: the negative electrode material is the negative electrode material for the aqueous magnesium ion battery described above or a Na2Ti2O5 thin film.

[0030] The sixth object of the present invention is to provide an aqueous magnesium ion battery. The battery includes a battery core and an aqueous electrolyte. The battery core and the aqueous electrolyte are sealed in a battery case. The battery core includes a positive electrode plate, a negative electrode plate, and a separator. Among them: the negative electrode plate is the negative electrode plate for the aqueous magnesium ion battery described above.

[0031] Further, in the above technical solution, the aqueous electrolyte is a conventional aqueous magnesium salt solution, including but not limited to an aqueous magnesium chloride solution, at least one of other conventional aqueous magnesium sulfate solutions, aqueous magnesium nitrate solutions, and aqueous magnesium acetate solutions, etc.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention explores the application of Na2Ti2O5 thin films and Na2Ti3O7 powders in conventional magnesium salt aqueous solutions. As the negative electrode of an aqueous magnesium-ion battery, the working potential range of the sodium titanate with a layered crystal structure described in the present invention is -1.7 to 0.4 V. Among them, the charge-discharge capacity of the Na2Ti2O5 half-cell is as high as 213 mAh / g at a current density of 2 A / g, and there is no obvious attenuation in capacity after 100 cycles at a current density of 10 A / g. The preparation method of the present invention is convenient, efficient, low-cost and highly repeatable, and has certain practical value. In addition, the present invention is of great significance for the development of negative electrode materials for aqueous magnesium-ion batteries, and can also be extended to the development of negative electrode materials for other ionic aqueous batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0035] Figure 1 It is the X-ray diffraction pattern and scanning electron microscope image of the Na2Ti2O5 thin film obtained in Example 1 of the present invention.

[0036] Figure 2 It is the X-ray diffraction and scanning electron microscope image of the Na2Ti3O7 powder obtained in Example 2 of the present invention.

[0037] Figure 3 It is the cyclic voltammogram of the Na2Ti2O5 half-cell obtained in Application Example 1 of the present invention in 1 mol / L magnesium chloride aqueous solution for the first five cycles and at different scan rates.

[0038] Figure 4 It is the charge-discharge curve of the Na2Ti2O5 half-cell obtained in Application Example 1 of the present invention for the first five cycles at a current density of 2 A / g.

[0039] Figure 5 It is the rate performance graph, charge-discharge curve graph and long-life cycle performance graph of the Na2Ti2O5 half-cell obtained in Application Example 1 of the present invention.

[0040] Figure 6 It is the cyclic voltammogram, rate performance and long-life cycle performance graph of the Na2Ti3O7 half-cell obtained in Application Example 2 of the present invention in 1 mol / L magnesium chloride aqueous solution. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The present invention uses sodium titanate with a layered crystal structure as the negative electrode material for aqueous magnesium ion batteries. Due to its excellent chemical and structural stability, sodium titanate with a layered crystal structure can achieve reversible Mg 2+ insertion / extraction in a conventional aqueous magnesium electrolyte. In the present invention, titanium foil / tetrabutyl titanate and sodium hydroxide solution are used as the titanium source and sodium source respectively, and Na2Ti2O5 thin film and Na2Ti3O7 powder are synthesized through simple hydrothermal and high-temperature annealing processes. In magnesium chloride electrolyte, both sodium titanate materials exhibit extremely low charge-discharge potentials (Na2Ti2O5, -1.3 to -0.6 V vs. SCE; Na2Ti3O7, -1.5 to -1 V vs. SCE) and good cycle stability. In addition, the Na2Ti2O5 half-cell has a charge-discharge specific capacity as high as 213 mAh / g at a current density of 2 A / g and still maintains a high specific capacity of 150 mAh / g at a high current density of 10 A / g. The sodium titanate with a layered crystal structure mentioned in the present invention is an ideal negative electrode material for aqueous magnesium batteries, and at the same time has the advantages of low cost and environmental friendliness, and has great application prospects in the field of aqueous magnesium ion energy storage.

[0042] The present invention will be further described in detail below through implementation cases. These implementation cases are implemented on the premise of the technology of the present invention, and the detailed implementation methods and specific operation processes are given to illustrate the creativity of the present invention, but the protection scope of the present invention is not limited to the following implementation cases.

[0043] Based on the information contained in this application, those skilled in the art can easily make various changes to the precise description of the present invention. It should be understood that the scope of the present invention is not limited to the defined processes, properties or components, because these implementation cases and other descriptions are only for illustrative purposes of specific aspects of the present invention.

[0044] In order to better understand the present invention rather than limit its scope, all numbers representing amounts, percentages, and other numerical values used in this application should be understood to be modified by the word "about" in all cases. Therefore, unless otherwise specified, the numerical parameters listed in the specification are approximate values, which may be changed according to different desired properties. Each numerical parameter should at least be regarded as obtained according to the reported significant figures and through the conventional rounding method.

[0045] The equipment and raw materials used in the present invention can be purchased from the market or are commonly used in the art. The methods in the following implementation cases are all conventional methods in the art unless otherwise specified.

[0046] In step (1) of Example 1 below, the specifications of the titanium foil are not limited to a thickness of 50 μm and a fixed area size; in step (2), the volume of the polystyrene black inner liner substrate is not limited to 100 mL, and the inner liner of the reaction kettle with a suitable volume size can be adjusted according to the specifications of the cut metal titanium foil.

[0047] Example 1

[0048] The Na2Ti2O5 thin film of this example is prepared by one-step hydrothermal synthesis followed by high-temperature annealing. The specific preparation method is as follows:

[0049] (1) A commercial titanium foil with an area of 5 cm * 10 cm and a thickness of 50 μm is polished with 320-mesh sandpaper until the surface has no obvious luster, then ultrasonically cleaned successively with acetone, absolute ethanol, and deionized water, and then placed in an 80 °C oven for drying treatment;

[0050] (2) The dried titanium foil is placed in a 100 mL polystyrene black inner liner containing a 1 mol / L aqueous sodium hydroxide solution, sealed, and the reaction kettle is placed in an 220 °C oven for 24 hours;

[0051] (3) The titanium foil with Na2Ti2O5 grown after the reaction in step (2) is taken out, washed and dried, then placed in a tube furnace and heated to 450 °C under the protection of a special gas atmosphere, and kept at 450 °C for 2 hours to obtain the Na2Ti2O5 thin film; where: the special gas atmosphere is composed of 5% (v / v) hydrogen and 95% (v / v) argon.

[0052] Structure and morphology testing:

[0053] The product prepared in Example 1 is subjected to phase analysis and morphological structure characterization. Figure 1 For the X-ray diffraction, optical, and scanning electron microscope images of the product prepared in Example 1. As Figure 1 shown in a, the synthesized material is Na2Ti2O5, and the positions of its diffraction peaks match the standard spectrum (PDF#47-0124) of titanic acid monohydrate (H2Ti2O5·H2O). Figure 1 b shows the optical and scanning electron microscope images of Na2Ti2O5. It can be seen from the scanning electron microscope image that its structure is nanowire-like.

[0054] Example 2

[0055] The preparation method of the Na2Ti3O7 powder in this example specifically includes the following steps:

[0056] (1) 20 mL of glycerol is dispersed in 100 mL of a 10 g / L tetrabutyl titanate aqueous solution, and vigorously stirred to mix evenly, then 50 mL of a 10 mol / L NaOH solution is slowly added and stirred evenly;

[0057] (2) Transfer the mixed solution obtained in step (1) to the inner lining of a stainless-steel autoclave, seal it, and hydrothermally treat it at 200 °C for 24 hours. Centrifuge the mixed solution, wash it, and collect the powder sample.

[0058] (3) Collect the dried white sample and place it under the protection of a special gas atmosphere and hold it at 450 °C for 2 hours to obtain Na2Ti3O7 powder; wherein: the special gas atmosphere is composed of 5% (v / v) hydrogen and 95% (v / v) argon.

[0059] Structure and morphology testing:

[0060] Perform phase analysis and morphological structure characterization on the powder product prepared in Example 2. Figure 2 Are the X-ray diffraction, optical, and scanning electron microscope images of the powder product prepared in Example 2. As shown in Figure 2 a, the synthesized material is Na2Ti3O7, and the positions of its diffraction peaks match the standard pattern (PDF#31-1329), with the space group P21 / m. Figure 2 b is the optical and scanning electron microscope images of the powder product prepared in Example 2. It can be seen from the scanning electron microscope images that its morphology shows sea urchin-like nanospheres.

[0061] The specific methods for cyclic voltammetry and constant current charge-discharge tests of the batteries involved in Application Example 1 and Application Example 2 below are as follows: Under the constant temperature condition of 25 °C, use a Wuhan Koster electrochemical workstation to perform linear cyclic voltammetry curve tests, and the potential window for testing is -1.7 to -0.4 V vs. SCE; for constant current charge-discharge tests, the test voltage range is -1.5 to -0.3 V vs. SCE, and the test current density is 2 to 20 A / g.

[0062] The specific composition and preparation method of the electrolyte involved in Application Example 1 and Application Example 2 below are as follows:

[0063] Using magnesium chloride (MgCl2) as the magnesium salt and deionized water as the solvent, add an appropriate amount of magnesium chloride to deionized water to prepare an aqueous MgCl2 solution with a molar concentration of 1 mol / L as the electrolyte.

[0064] Application Example 1

[0065] Cut the Na2Ti2O5 film prepared in Example 1 into appropriate sizes (1 cm × 0.5 cm). Scrape off part of the surface Na2Ti2O5 film with a surgical blade, and then connect it to a titanium metal foil current collector as the negative electrode plate of an aqueous magnesium-ion battery; use a three-electrode system to test the electrochemical performance of the sodium titanate negative electrode, where the counter electrode and reference electrode are a platinum wire electrode and a saturated calomel electrode, respectively.

[0066] Assemble the prepared Na2Ti2O5 negative electrode sheet, electrolyte, platinum sheet electrode, saturated calomel electrode, and others such as glass containers, test brackets, and electrode wires into an aqueous magnesium-ion half-cell test device, namely the Na2Ti2O5 half-cell.

[0067] Figure 3 Figures a and b respectively show the linear cyclic voltammograms of the Na2Ti2O5 half-cell obtained in this application example at a scan rate of 10 mV / s for the first five cycles and at 2 - 10 mV / s. It can be seen that a pair of obvious redox peaks can be observed at the potentials of -1.2 V / -1.65 V, and with the increase of the scan rate, which indicates that the Na2Ti2O5 negative electrode has reversible electrochemical magnesium insertion / extraction performance.

[0068] Figure 4 Shows the charge-discharge curves of the Na2Ti2O5 half-cell obtained in this application example for the first five cycles at a charge-discharge current density of 2 A / g. It can be seen that the Na2Ti2O5 negative electrode gradually becomes stable after 5 cycles of activation, and exhibits a high reversible capacity (210 mAh / g) and a low working potential (-1.2 V vs. SCE) at a current density of 2 A / g.

[0069] Figure 5 Is the rate and cycle performance diagram of the Na2Ti2O5 half-cell obtained in this application example at different current densities. As shown in Figure 5 a - b, the Na2Ti2O5 half-cell obtained in this application example can maintain a stable specific capacity at different current densities. When the current density returns to the minimum current, the capacity only shows a little attenuation. In addition, the Na2Ti2O5 half-cell still maintains a high specific capacity of 150 mAh / g at a high current density of 10 A / g, indicating its excellent rate cycling performance. Figure 5 In c, the Na2Ti2O5 half-cell has a cycle number of up to 100 times at a current density of 10 A / g, and after 20 cycles of activation in the first 20 cycles, only shows a capacity attenuation of 0.13% per cycle in the subsequent 80 cycles, demonstrating excellent cycle stability.

[0070] Application Example 2

[0071] Use the Na2Ti3O7 powder prepared in Example 2 as the negative electrode active material. Mix 7 mg of the Na2Ti3O7 powder with 2 mg of Ketjen black and 1 mg of polytetrafluoroethylene, and add 2 mL of isopropanol and stir evenly to obtain a slurry; then use a roll press to roll the slurry into a 10 cm * 10 cm thin film and dry it; then cut it into 1 cm * 1 cm pieces and directly cast it on a titanium mesh as the negative electrode sheet of the aqueous magnesium-ion battery; use a three-electrode system to test the electrochemical performance of the sodium titanate negative electrode, where the counter electrode and the reference electrode are a platinum wire electrode and a saturated calomel electrode respectively.

[0072] Assemble the prepared Na2Ti3O7 negative electrode sheet, electrolyte, platinum sheet electrode, saturated calomel electrode, and other components such as glass containers, test brackets, and electrode wires into an aqueous magnesium ion half-cell test device to obtain the Na2Ti3O7 half-cell.

[0073] Use the same test method as in Application Example 1 to test the electrochemical performance of the Na2Ti3O7 half-cell of this application example.

[0074] Figure 6 It is the cyclic voltammetry curve, rate performance, and cycling performance diagram of the Na2Ti3O7 half-cell obtained in this application example. As can be seen from Figure 6 a, Na2Ti3O7 shows redox peaks similar to those of Na2Ti2O5 in an aqueous magnesium chloride solution. As shown in Figure 6 b-c, the Na2Ti3O7 half-cell has a discharge specific capacity as high as 150 mAh / g at 2 A / g, and can be stably cycled 100 times at a current density of 10 A / g. After 30 cycles of capacity stabilization, only 0.41% of capacity decay is shown in each of the subsequent 70 cycles.

Claims

1. A sodium titanate with a layered crystal structure, characterized in that: The molecular formula of the sodium titanate is Na2Ti n O 2n+1 , where 2 ≤ n ≤ 3 and n is an integer.

2. The sodium titanate with a layered crystal structure according to claim 1, characterized in that: The sodium titanate with a layered crystal structure is Na2Ti2O5 or Na2Ti3O7.

3. The sodium titanate having a layered crystal structure according to claim 2, characterized in that: The Na2Ti2O5 is nanowire-shaped; the Na2Ti3O7 is a sea urchin-shaped nanomicrosphere.

4. The preparation method of Na2Ti2O5 according to claim 3, characterized in that: It includes the following steps: Put the clean and dry titanium substrate into the inner liner of a high-pressure reactor filled with sodium hydroxide solution, seal it, and then heat the sealed reactor to 220 °C for isothermal reaction for 24 hours; after the reaction is completed, take out the titanium substrate, dry it and place it in a tube furnace, and heat it to 450 °C for isothermal annealing for 2 hours in a special gas atmosphere to obtain a Na2Ti2O5 film.

5. The preparation method of Na2Ti3O7 according to claim 3, characterized in that: It includes the following steps: Disperse glycerol evenly in the aqueous solution of the titanium source according to the ratio, and then continue to drop the sodium hydroxide solution into the obtained mixed solution according to the ratio to obtain a reaction solution; transfer the reaction solution to the inner liner of a high-pressure reactor, seal it, and then heat the sealed reactor to 200 °C for isothermal reaction for 24 hours; after the reaction is completed, centrifuge the obtained product, collect the precipitate, dry it and place it in a tube furnace, and heat it to 450 °C for isothermal annealing for 2 hours in a special gas atmosphere to obtain Na2Ti3O7 powder.

6. Application of the sodium titanate with a layered crystal structure according to any one of claims 1-3 in an aqueous magnesium ion battery.

7. An anode material for an aqueous magnesium-ion battery, the anode material comprising an anode active material, conductive carbon black, and a binder, characterized in that: The negative electrode active material is the Na2Ti3O7 powder prepared by the method according to claim 5.

8. A negative electrode sheet for an aqueous magnesium ion battery, the negative electrode sheet comprising a current collector and a negative electrode material coated and / or filled on the current collector, characterized in that: The negative electrode material is the negative electrode material of the aqueous magnesium ion battery according to claim 7 or the Na2Ti2O5 film prepared by the method according to claim 4.

9. A water-based magnesium ion battery, the battery comprising a core and a water-based electrolyte, the core and the water-based electrolyte being sealed within a battery housing, the core comprising a positive electrode sheet, a negative electrode sheet and a separator, characterized in that: The negative electrode plate is the negative electrode plate of the aqueous magnesium ion battery according to claim 8.

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