A Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material, preparation method and application thereof

Abstract

This invention discloses a Na2Ti7O 15 Na₂Ti₃O₇ sodium titanate electrode material, its preparation method, and its application. This electrode material is a porous, blocky structure composed of stacked nanorods. It is synthesized by a simple solid-state method, where sodium carbonate precursor and anatase titanium dioxide are ball-milled in a specific ratio and then microwave-sintered in air. 15 The addition of [a specific ingredient] increases the exposure of the (100) sodium storage crystal face in Na2Ti3O7 sodium titanate, while decreasing the exposure of the (003) crystal face; Na2Ti7O 15 The presence of four TiO6 octahedrons within a single structural unit increases the number of sodium storage sites and widens the sodium ion diffusion channels, thereby improving the material's specific capacity and rate performance. (Na2Ti7O) 15 The two layers of TiO6 octahedrons are interconnected, making the structure more stable during sodium ion insertion / extraction, thereby increasing the long-term cycling stability of the material.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material and preparation method and application thereof. BACKGROUND

[0002] In recent years, lithium ion batteries have achieved great success in the field of portable electronic devices and electric vehicles, leading to an increasing demand for lithium resources. With a substantial increase in the cost of lithium resources, sodium ion batteries are considered to be an ideal substitute for lithium ion batteries due to their abundant resources, low cost and high efficiency. For sodium ion batteries, a large number of electrode materials have been explored, but there is a serious lack of low-voltage negative electrode materials comparable to graphite negative electrodes in lithium ion batteries. Titanium-based materials have attracted widespread research interest as negative electrode materials for sodium ion batteries due to their rich crystal forms, moderate Ti 3+ / Ti 4+ low potential redox couples, and low cost.

[0003] Among various titanium-based negative electrode materials for sodium ion batteries, Na2Ti3O7 is considered to be a very promising negative electrode material due to its special zigzag layer structure of titanium-oxygen octahedra, an average low-sodium intercalation platform of 0.3 V (vs. Na / Na + ) and a theoretical specific capacity of 177 mAh g -1 . Studies have found that the electronic conductivity and sodium ion diffusion coefficient of Na2Ti3O7 are not high, and in order to meet the principle of minimum energy, sodium ions prefer to migrate along these zigzag layers rather than across these layers, so the number and length of sodium ion migration channels and the stability of the channels are key factors restricting the migration and intercalation / deintercalation of sodium ions in Na2Ti3O7.

[0004] In recent years, in order to shorten the sodium ion migration path, widen the ion diffusion channel and stabilize the interlayer structure during charging and discharging, nanocrystallization design and doping of other elements on Na2Ti3O7 are a mainstream strategy, but nanocrystallization preparation methods are often high in cost and low in yield, which is difficult to realize in industrial production, and simple ion doping cannot well improve the structural collapse problem caused by the sliding and expansion of the layered material during charging and discharging.

[0005] The patent application of the research group, a kind of potassium-doped sodium titanate electrode material and its preparation method and application (202211220673.9), is to dope sodium titanate electrode material with potassium ions. Due to the presence of potassium ions, pure phase potassium-doped Na2Ti3O7 crystal phase is obtained after calcination, and part of the sodium ions in the Na2Ti3O7 crystal phase are replaced by potassium ions, which is a method of shortening the sodium ion migration path by ion doping.

[0006] The application adopts a completely different doping direction, adopts a crystal phase doping method, and increases sodium ion storage sites, widens sodium ion diffusion channels, and stabilizes structure changes in the charging and discharging process by doping Na2Ti7O 15 Doping Na2Ti3O7 sodium titanate electrode material and its preparation method and application. SUMMARY

[0007] In view of the problems in the prior art, the application provides a Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material and its preparation method and application.

[0008] To achieve the above object, the application provides the following technical scheme.

[0009] A Na2Ti7O 15 The doped Na2Ti3O7 sodium titanate electrode material has a porous block structure formed by stacking nanorods, and the diameter is 100-400 nm.

[0010] Preferably, the Na2Ti7O 15 The crystal phase is regularly doped in the Na2Ti3O7 crystal phase.

[0011] Microwave-assisted Na2Ti7O 15 The doped Na2Ti3O7 sodium titanate negative electrode material has a preferred orientation, the (100) crystal plane is exposed more, and the (003) crystal plane is exposed less. The existence of the Na2Ti7O 15 The existence of the Na2Ti7O

[0012] The application also provides a method for preparing the Na2Ti7O 15 doped Na2Ti3O7 sodium titanate electrode material, which comprises the following steps.

[0013] (1) Ball-milling and mixing sodium carbonate and anatase titanium dioxide to obtain a uniformly mixed precursor mixture;

[0014] (2) placing the uniformly mixed precursor mixture in a microwave tube furnace and calcining in an air atmosphere to obtain the Na2Ti7O 15 doped Na2Ti3O7 sodium titanate electrode material.

[0015] Preferably, the molar ratio of the sodium carbonate to the anatase titanium dioxide is (1.5-1.99):6.

[0016] Preferably, the heating rate of calcination in the microwave tube furnace is 5-10℃ / min, the calcination temperature is 800-1100℃, and the calcination time is 20-60min.

[0017] In addition, the application also provides the Na2Ti7O 15 Application of the doped Na2Ti3O7 sodium titanate electrode material in a sodium ion battery.

[0018] The beneficial effects of the application are as follows:

[0019] (1) The precursor of the electrode material is low-cost sodium carbonate and titanium dioxide;

[0020] (2) The preparation method of the material is simple, the precursor is ball milled according to the proportion, and then microwave sintering is carried out in the air to obtain the doped sodium titanate electrode material, and the sodium titanate electrode material can be obtained by reducing the proportion of sodium carbonate;

[0021] (3) The Na2Ti7O 15 The doped Na2Ti3O7 sodium titanate is used as a negative electrode material and applied to a sodium ion battery, and due to the addition of Na2Ti7O 15 , the exposure of the Na2Ti3O7 sodium titanate (100) sodium storage crystal surface increases, and the exposure of the (003) crystal surface decreases. At the same time, due to the presence of four TiO6 octahedrons in one structural unit of Na2Ti7O 15 , compared with three TiO6 octahedrons in one structural unit of Na2Ti3O7, the sodium ion diffusion channel is wider, so that the specific capacity and rate performance of the material are improved. Compared with the TiO6 octahedrons separated in the upper and lower layers of the Na2Ti3O7 layered material, the upper and lower layers of the TiO6 octahedrons are connected to each other, and the structure is more stable during the sodium ion intercalation / deintercalation process, thereby increasing the long cycle stability of the material. 15 BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The field emission scanning electron microscope image of the Na2Ti7O 15 doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7&Na2Ti7O 15 The X-ray diffraction pattern of the Na2Ti3O7 sodium titanate electrode material prepared in Comparative Example 1.

[0023] Figure 2 The field emission scanning electron microscope image of the Na2Ti7O 15 doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7&Na2Ti7O 15 . ​

[0024] Figure 3 Na2Ti7O 15 Doped Na2Ti307 sodium titanate electrode material 1.9 Na2Ti307 & Na2Ti7O 15 High-angle annular dark-field scanning transmission electron microscopy image of the

[0025] Figure 4 Na2Ti7O 15 Doped Na2Ti307 sodium titanate electrode material 1.5 Na2Ti307 & Na2Ti7O 15 First charge-discharge voltage vs. specific capacity plot of the

[0026] Figure 5 Na2Ti7O 15 Doped Na2Ti307 sodium titanate electrode material 1.6 Na2Ti307 & Na2Ti7O 15 First charge-discharge voltage vs. specific capacity plot of the

[0027] Figure 6 Na2Ti7O 15 Doped Na2Ti307 sodium titanate electrode material 1.7 Na2Ti307 & Na2Ti7O 15 First charge-discharge voltage vs. specific capacity plot of the

[0028] Figure 7 Na2Ti7O 15 Doped Na2Ti307 sodium titanate electrode material 1.8 Na2Ti307 & Na2Ti7O 15 First charge-discharge voltage vs. specific capacity plot of the

[0029] Figure 8 Na2Ti7O 15 Doped Na2Ti307 sodium titanate electrode material 1.9 Na2Ti307 & Na2Ti7O 15 First charge-discharge voltage vs. specific capacity plot of the

[0030] Figure 9 Na2Ti7O 15 Doped Na2Ti307 sodium titanate electrode material 1.99 Na2Ti307 & Na2Ti7O 15 First charge-discharge voltage vs. specific capacity plot of the

[0031] Figure 10 First charge-discharge voltage vs. specific capacity plot of the Na2Ti307 sodium titanate electrode material prepared for Comparative Example 1.

[0032] Figure 11 Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7 & Na2Ti7O 15 Rate capability plot of Na2Ti3O7 sodium titanate electrode material prepared in Comparative Example 1 (circle: Example 5; triangle: Comparative Example 1). DETAILED DESCRIPTION

[0033] In order for those skilled in the art to better understand the technical solutions of the present application, the technical solutions of the present application will be described clearly and completely below in combination with the drawings of the present application. Based on the examples in the present application, other similar examples obtained by those skilled in the art without making creative efforts shall all belong to the protection scope of the present application.

[0034] Example 1:

[0035] This example relates to Na2Ti7O 15 The preparation method of the doped Na2Ti3O7 sodium titanate electrode material comprises the following steps: at room temperature, 0.795 g of sodium carbonate and 2.396 g of anatase titanium dioxide (the molar ratio of sodium carbonate to anatase titanium dioxide is 1.5:6) are placed in a high-energy ball mill pot for ball milling for 1 hour to obtain a uniformly mixed precursor; then the precursor is placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 5 degrees Celsius per minute, and the precursor is calcined at 800 degrees Celsius in an air atmosphere for 60 minutes to obtain Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material (1.5Na2Ti3O7 & Na2Ti7O 15 ).

[0036] Example 2:

[0037] This example relates to Na2Ti7O 15 The preparation method of the doped Na2Ti3O7 sodium titanate electrode material comprises the following steps: at room temperature, 0.848 g of sodium carbonate and 2.396 g of anatase titanium dioxide (the molar ratio of sodium carbonate to anatase titanium dioxide is 1.6:6) are placed in a high-energy ball mill pot for ball milling for 1 hour to obtain a uniformly mixed precursor; then the precursor is placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 6 degrees Celsius per minute, and the precursor is calcined at 850 degrees Celsius in an air atmosphere for 50 minutes to obtain Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material (1.6Na2Ti3O7 & Na2Ti7O 15 ).

[0038] Example 3:

[0039] This embodiment relates to Na2Ti7O 15 The preparation method of the doped Na2Ti3O7 sodium titanate electrode material comprises the following steps: 0.901g of sodium carbonate and 2.396g of anatase titanium dioxide (the molar ratio of sodium carbonate to anatase titanium dioxide is 1.7:6) are placed in a high-energy ball mill tank for ball milling at room temperature for 1 hour to obtain a uniformly mixed precursor; then the precursor is placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 7 degrees Celsius per minute, and the precursor is calcined at 900 degrees Celsius in an air atmosphere for 40 minutes to obtain Na2Ti7O 15 The doped Na2Ti3O7 sodium titanate electrode material (1.7Na2Ti3O7 & Na2Ti7O 15 ) is obtained.

[0040] Example 4:

[0041] This embodiment relates to Na2Ti7O 15 The preparation method of the doped Na2Ti3O7 sodium titanate electrode material comprises the following steps: 0.901g of sodium carbonate and 2.396g of anatase titanium dioxide (the molar ratio of sodium carbonate to anatase titanium dioxide is 1.7:6) are placed in a high-energy ball mill tank for ball milling at room temperature for 1 hour to obtain a uniformly mixed precursor; then the precursor is placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 7 degrees Celsius per minute, and the precursor is calcined at 900 degrees Celsius in an air atmosphere for 40 minutes to obtain Na2Ti7O 15 The doped Na2Ti3O7 sodium titanate electrode material (1.7Na2Ti3O7 & Na2Ti7O 15 ) is obtained.

[0042] Example 5:

[0043] This embodiment relates to Na2Ti7O 15 The preparation method of the doped Na2Ti3O7 sodium titanate electrode material comprises the following steps: 0.901g of sodium carbonate and 2.396g of anatase titanium dioxide (the molar ratio of sodium carbonate to anatase titanium dioxide is 1.7:6) are placed in a high-energy ball mill tank for ball milling at room temperature for 1 hour to obtain a uniformly mixed precursor; then the precursor is placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 7 degrees Celsius per minute, and the precursor is calcined at 900 degrees Celsius in an air atmosphere for 40 minutes to obtain Na2Ti7O 15 The doped Na2Ti3O7 sodium titanate electrode material (1.7Na2Ti3O7 & Na2Ti7O 15 ) is obtained.

[0044] The Na2Ti7O 15Doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7 & Na2Ti7O 15 The material was characterized. The structure of the material was characterized by an X-ray diffractometer, and the results are shown in Figure 1 From Figure 1 it can be seen that the diffraction peaks of the prepared material are consistent with the crystal phase represented by the DFT standard card of Na2Ti3O7 and Na2Ti7O 15 , indicating that the Na2Ti7O 15 doped Na2Ti3O7 sodium titanate material (1.9Na2Ti3O7 & Na2Ti7O 15 ) is successfully prepared. In Figure 1 , the diffraction intensity of the 10.527° (100) crystal plane is enhanced, and the diffraction intensity of the 29.929° (003) crystal plane is relatively reduced, indicating that the addition of Na2Ti7O 15 causes the preferred orientation of the crystal, so that the exposure of the (100) crystal plane increases and the exposure of the (003) crystal plane relatively decreases, which makes the diffusion channel of sodium ions increase at the same time and become shorter. It is beneficial to the diffusion and storage of sodium ions.

[0045] The morphology of the 1.9Na2Ti3O7 & Na2Ti7O 15 material was characterized by field emission scanning electron microscopy (FE-SEM), and the results are shown in Figure 2 From Figure 2 it can be seen that the prepared material is a porous block structure accumulated by nanorods, and the rod diameter is 100-400 nm.

[0046] The 1.9Na2Ti3O7 & Na2Ti7O 15 material was characterized by high-angle annular dark-field spherical aberration correction scanning transmission electron microscopy (HAADF-STEM), and the results are shown in Figure 3 From Figure 3 it can be seen that the Na2Ti7O 15 crystal phase regularly appears in the Na2Ti3O7 crystal phase, indicating that the Na2Ti7O 15 is successfully doped into the Na2Ti3O7 crystal phase. Since there are 4 TiO6 octahedra in a structural unit of Na2Ti7O 15 , compared with 3 TiO6 octahedra in a structural unit of Na2Ti3O7, it has more sodium storage sites and wider sodium ion diffusion channels, thereby improving the specific capacity and rate performance of the material. Compared with the TiO6 octahedra separated by two layers in the Na2Ti3O7 layered material, the Na2Ti7O 15The two TiO6 octahedral layers are interconnected, making the structure more stable during sodium ion insertion / extraction, thus increasing the long-term cycling stability of the material.

[0047] Example 6:

[0048] This embodiment involves Na2Ti7O 15 The preparation method of Na2Ti3O7-doped sodium titanate electrode material includes the following steps: At room temperature, 1.054 g of sodium carbonate and 2.396 g of anatase titanium dioxide (the molar ratio of sodium carbonate to anatase titanium dioxide is 1.99:6) are placed in a high-energy ball mill jar and ball-milled for 1 hour to obtain a homogeneous precursor. Then, the precursor is placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 10 degrees Celsius / min, and calcination is carried out at 1100 degrees Celsius in air atmosphere for 20 minutes to obtain Na2Ti3O7-doped sodium titanate electrode material. 15 Sodium titanate electrode material doped with Na2Ti3O7 (1.99Na2Ti3O7 & Na2Ti7O) 15 ).

[0049] Comparative Example 1:

[0050] This embodiment relates to a method for preparing pure-phase Na2Ti3O7 sodium titanate electrode material. The steps are as follows: at room temperature, 1.060g of sodium carbonate and 2.396g of anatase phase titanium dioxide are placed in a high-energy ball mill jar and ball-milled for 1 hour to obtain a uniformly mixed precursor; then the precursor is placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 10 degrees Celsius / minute, and calcination is carried out at 850 degrees Celsius in air atmosphere for 20 minutes to obtain sodium titanate electrode material (Na2Ti3O7).

[0051] The Na2Ti3O7 sodium titanate electrode material prepared in this embodiment was characterized by X-ray diffraction, and the results are as follows: Figure 1 As shown. From Figure 1 As can be seen, the diffraction peaks of the prepared material are consistent with the crystal phase represented by the DFT standard card of Na2Ti3O7, indicating that pure-phase Na2Ti3O7 sodium titanate material was successfully prepared in this embodiment. Regarding Na2Ti7O 15 The specific steps for testing the electrochemical performance of Na2Ti3O7-doped sodium titanate electrode materials are as follows:

[0052] The Na2Ti7O obtained in Examples 1-6 15Using Na2Ti3O7-doped sodium titanate material and the Na2Ti3O7-doped sodium titanate electrode material obtained in Comparative Example 1 as the negative electrode of a sodium-ion battery, metallic sodium as the counter electrode, glass fiber as the separator, and sodium perchlorate (NaPF6) as the electrolyte, the batteries were encapsulated in an argon-atmosphere glove box using a CR2032 coin cell casing to obtain Na2Ti7O7-doped sodium titanate. 15 Half-cells using Na₂Ti₃O₇ sodium titanate electrode materials and half-cells using Na₂Ti₃O₇ sodium titanate electrode materials. At 0.1C (1C = 177 mA g / g). -1 Electrochemical performance was tested at 0.1, 0.2, 0.5, 1, 2, 5, 10, and 20C rates within the 0.01-2.5V voltage range, and the specific capacitance is shown in Table 1. Electrochemical rate performance was also tested at 0.1, 0.2, 0.5, 1, 2, 5, 10, and 20C rates within the 0.01-2.5V voltage range, and the rate performance is shown in Table 1. Figure 11 As shown.

[0053] Table 1 Examples 1-6 Na2Ti7O 15 The specific charge capacity (mAh g) of the sodium titanate electrode material doped with Na2Ti3O7 and the sodium titanate electrode material of Comparative Example 1 -1 ).

[0054]

[0055] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A Na₂Ti₇O 15 Na₂Ti₃O₇ sodium titanate electrode material, characterized in that, Its structure is a porous block structure made up of stacked nanorods with a diameter of 100-400 nm.

2. The sodium titanate electrode material according to claim 1, characterized in that, Na2Ti7O 15 The crystal phase is regularly doped in the Na2Ti3O7 crystal phase.

3. A method for preparing Na₂Ti₇O as described in claim 1 or 2 15 The method for using sodium titanate electrode materials doped with Na2Ti3O7 is characterized by, Includes the following steps: (1) Sodium carbonate and anatase phase titanium dioxide were ball-milled to obtain a uniformly mixed precursor mixture; (2) The homogeneous precursor mixture was placed in a microwave tube furnace and calcined in an air atmosphere to obtain Na2Ti7O. 15 Sodium titanate electrode material doped with Na2Ti3O7.

4. The Na₂Ti₇O₇ according to claim 3 15 A method for preparing Na₂Ti₃O₇ sodium titanate electrode material, characterized in that... The molar ratio of sodium carbonate to anatase titanium dioxide is (1.50–1.99):

6.

5. The Na₂Ti₇O according to claim 3 15 A method for preparing Na₂Ti₃O₇ sodium titanate electrode material, characterized in that... The heating rate for calcination in the microwave tube furnace is 5–10 °C / min, the calcination temperature is 800–1100 °C, and the calcination time is 20–60 min.

6. The Na₂Ti₇O as described in claim 1 or 2 15 Application of Na2Ti3O7 doped sodium titanate electrode material in sodium-ion batteries.

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