Na 2ti 7o 15 doped na 2ti 3o 7 sodium titanate electrode material, and preparation method therefor and use thereof

Abstract

A Na2Ti7O15 doped Na2Ti3O7 sodium titanate electrode material, and a preparation method therefor and a use thereof. The electrode material has a porous block structure formed by stacking nanorods. The electrode material is synthesized by a simple solid-phase method, and is obtained by carrying out ball milling on precursors sodium carbonate and anatase-phase titanium dioxide in proportion, and then carrying out microwave sintering in air; the addition of Na2Ti7O15 increases the exposure of (100) sodium storage crystal face and decreases the exposure of (003) crystal face of Na2Ti3O7 sodium titanate; and Na2Ti7O15 has four TiO6 octahedrons in one structural unit, and has more sodium storage sites and wider sodium-ion diffusion channels, thereby improving the specific capacity and rate performance of the material. Upper and lower layers of TiO6 octahedrons in Na2Ti7O15 are connected to each other, such that the structure is more stable in a sodium-ion intercalation / deintercalation process, thereby improving the long cycle stability of the material.

Description

A Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material and its preparation method and application Technical Field

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

[0002] In recent years, lithium-ion batteries have achieved great success in the fields of portable electronic devices and electric vehicles, resulting in an increasing demand for lithium resources. With the substantial increase in the cost of lithium resources, sodium-ion batteries are considered to be an ideal alternative to 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 that can be comparable to the graphite negative electrode in lithium-ion batteries. Titanium-based materials have a rich crystal structure and moderate Ti 3+ / Ti 4+ The low potential redox couple and low cost have attracted extensive research interest as negative electrode materials for sodium-ion batteries.

[0003] Among various titanium-based negative electrode materials for sodium ion batteries, Na2Ti3O7 has a unique zigzag layered structure of titanium oxide octahedrons and a high resistance to 0.3V (vs. Na / Na + ) average low sodium embedded platform and 177 mAh g -1 The theoretical specific capacity of Na2Ti3O7 is considered to be a very promising negative electrode material. 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 through them. Therefore, the number and length of sodium ion migration channels and the stability of the channels are key factors restricting the migration and insertion / extraction 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, nano-designing and doping Na2Ti3O7 with other elements has become a mainstream strategy. However, the nano-sizing preparation method is often costly and has a very low yield, which is difficult to achieve in industrial production. Simple ion doping cannot effectively improve the structural collapse problem caused by structural slip and expansion of layered materials during charging and discharging.

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

[0006] However, this application adopts a completely different doping direction, using the crystal phase doping method to dope Na2Ti7O 15 This strategy of doping Na2Ti3O7 into the crystalline phase to increase sodium ion storage sites, broaden sodium ion diffusion channels, and stabilize structural changes during charge and discharge is previously unreported. Furthermore, this strategy utilizes a microwave-assisted solid-phase synthesis method. The preparation method is simple, has high yields, and is readily scalable to industrial production.

[0007] Summary of the Invention

[0008] In view of the problems existing in the above-mentioned prior art, the present invention provides a Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material, preparation method and application thereof.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A Na2Ti7O 15 The sodium titanate electrode material doped with Na2Ti3O7 has a porous block structure formed by the accumulation of nanorods with a diameter of 100-400nm.

[0011] Preferably, Na2Ti7O 15 The crystal phase is regularly doped in the Na2Ti3O7 crystal phase.

[0012] Microwave-assisted Na2Ti7O 15 Doping Na2Ti3O7 sodium titanate negative electrode material, the preferred orientation occurs, the (100) crystal plane exposure increases, while the (003) crystal plane exposure decreases. 15 The presence of increases the sodium storage sites of the material and broadens the diffusion channels of sodium ions, which can stabilize the interlayer structure during the charge and discharge process.

[0013] The present invention also provides a method for preparing the above-mentioned Na2Ti7O 15 The method of doping Na2Ti3O7 sodium titanate electrode material comprises the following steps:

[0014] (1) ball milling sodium carbonate and anatase phase titanium dioxide to obtain a uniform precursor mixture;

[0015] (2) The uniformly mixed precursor mixture is placed in a microwave tube furnace and calcined in an air atmosphere to obtain Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material.

[0016] Preferably, the molar ratio of sodium carbonate to anatase phase titanium dioxide is (1.5-1.99):6.

[0017] Preferably, the heating rate of 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.

[0018] In addition, the present invention also provides the above-mentioned Na2Ti7O 15 Application of doped Na2Ti3O7 sodium titanate electrode materials in sodium ion batteries.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) The precursors of the electrode materials are low-cost sodium carbonate and titanium dioxide;

[0021] (2) The preparation method of the material is simple. It adopts the solid phase method to synthesize. After the precursor is ball-milled in proportion, it is obtained by microwave sintering in air. By reducing the proportion of sodium carbonate, the phase-doped sodium titanate electrode material can be obtained.

[0022] (3) Na2Ti7O 15 Doped sodium titanate Na2Ti3O7 is used as negative electrode material in sodium ion batteries. 15 The addition of Na2Ti3O7 increases the exposure of the sodium storage crystal face (100) and reduces the exposure of the (003) crystal face. 15 There are 4 TiO6 octahedrons in one structural unit, compared with 3 TiO6 octahedrons in one structural unit of Na2Ti3O7, which has more sodium storage sites and wider sodium ion diffusion channels, thereby improving the specific capacity and rate performance of the material. 15 The upper and lower layers of TiO6 octahedrons are connected to each other, making their structure more stable during the sodium ion insertion / extraction process, thereby increasing the long-cycle stability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 shows the Na2Ti7O prepared in Example 5. 15 Doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7&Na2Ti7O 15And the X-ray diffraction pattern of Na2Ti3O7 sodium titanate electrode material prepared in Comparative Example 1.

[0024] Figure 2 shows the Na2Ti7O prepared in Example 5. 15 Doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7&Na2Ti7O 15 Field emission scanning electron microscopy image.

[0025] Figure 3 shows the Na2Ti7O prepared in Example 5. 15 Doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7&Na2Ti7O 15 High-angle annular dark-field spherical aberration-corrected scanning transmission electron microscopy image.

[0026] Figure 4 shows the Na2Ti7O prepared in Example 1 15 Doped Na2Ti3O7 sodium titanate electrode material 1.5Na2Ti3O7&Na2Ti7O 15 The first charge and discharge voltage and specific capacity diagram.

[0027] Figure 5 shows the Na2Ti7O prepared in Example 2 15 Doped Na2Ti3O7 sodium titanate electrode material 1.6Na2Ti3O7&Na2Ti7O 15 The first charge and discharge voltage and specific capacity diagram.

[0028] Figure 6 shows the Na2Ti7O prepared in Example 3 15 Doped Na2Ti3O7 sodium titanate electrode material 1.7Na2Ti3O7&Na2Ti7O 15 The first charge and discharge voltage and specific capacity diagram.

[0029] Figure 7 shows the Na2Ti7O prepared in Example 4. 15 Doped Na2Ti3O7 sodium titanate electrode material 1.8Na2Ti3O7&Na2Ti7O 15 The first charge and discharge voltage and specific capacity diagram.

[0030] Figure 8 shows the Na2Ti7O prepared in Example 5. 15 Doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7&Na2Ti7O 15 The first charge and discharge voltage and specific capacity diagram.

[0031] Figure 9 shows the Na2Ti7O prepared in Example 6. 15 Doped Na2Ti3O7 sodium titanate electrode material 1.99Na2Ti3O7&Na2Ti7O 15 The first charge and discharge voltage and specific capacity diagram.

[0032] FIG10 is a graph showing the first charge and discharge voltage and specific capacity of the Na2Ti3O7 sodium titanate electrode material prepared in Comparative Example 1.

[0033] Figure 11 shows the Na2Ti7O prepared in Example 5. 15 Doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7&Na2Ti7O 15 and the rate performance diagram of the Na2Ti3O7 sodium titanate electrode material prepared in Comparative Example 1 (circles: Example 5; triangles: Comparative Example 1). DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings of the present invention. Based on the embodiments in this application, other similar embodiments obtained by ordinary technicians in this field without making any creative work should fall within the scope of protection of this application.

[0035] Example 1:

[0036] This embodiment involves Na2Ti7O 15 The preparation method of the sodium titanate electrode material doped with Na2Ti3O7 comprises the following steps: at room temperature, 0.795g of sodium carbonate and 2.396g of anatase phase titanium dioxide (the molar ratio of sodium carbonate to anatase phase titanium dioxide is 1.5:6) are placed in a high-energy ball mill for 1 hour to obtain a uniformly mixed precursor; the precursor is then 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 ).

[0037] Example 2:

[0038] This embodiment involves Na2Ti7O 15 The preparation method of the sodium titanate electrode material doped with Na2Ti3O7 comprises the following steps: at room temperature, 0.848g of sodium carbonate and 2.396g of anatase phase titanium dioxide (the molar ratio of sodium carbonate to anatase phase titanium dioxide is 1.6:6) are placed in a high-energy ball mill for 1 hour to obtain a uniformly mixed precursor; the precursor is then 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&Na2Ti7O15 ).

[0039] Example 3:

[0040] This embodiment involves Na2Ti7O 15 The preparation method of the sodium titanate electrode material doped with Na2Ti3O7 comprises the following steps: at room temperature, 0.901 g of sodium carbonate and 2.396 g of anatase phase titanium dioxide (the molar ratio of sodium carbonate to anatase phase titanium dioxide is 1.7:6) are placed in a high-energy ball mill for 1 hour to obtain a uniformly mixed precursor; the precursor is then 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 Doped Na2Ti3O7 sodium titanate electrode material (1.7Na2Ti3O7&Na2Ti7O 15 ).

[0041] Example 4:

[0042] This embodiment involves Na2Ti7O 15 The preparation method of the sodium titanate electrode material doped with Na2Ti3O7 comprises the following steps: at room temperature, 0.954g of sodium carbonate and 2.396g of anatase phase titanium dioxide (the molar ratio of sodium carbonate to anatase phase titanium dioxide is 1.8:6) are placed in a high-energy ball mill for 1 hour to obtain a uniformly mixed precursor; the precursor is then placed in a microwave tube furnace for high-temperature calcination, specifically, the heating rate is set to 8 degrees Celsius per minute, and the precursor is calcined at 1000 degrees Celsius in an air atmosphere for 30 minutes to obtain Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material (1.8Na2Ti3O7&Na2Ti7O 15 ).

[0043] Example 5:

[0044] This embodiment involves Na2Ti7O 15 The preparation method of the sodium titanate electrode material doped with Na2Ti3O7 comprises the following steps: 1.007g of sodium carbonate and 2.396g of anatase phase titanium dioxide (the molar ratio of sodium carbonate to anatase phase titanium dioxide is 1.9:6) are placed in a high-energy ball mill for 1 hour at room temperature to obtain a uniformly mixed precursor; the precursor is then placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 10 degrees Celsius per minute, and the precursor is calcined at 850 degrees Celsius in an air atmosphere for 20 minutes to obtain Na2Ti7O7. 15 Doped Na2Ti3O7 sodium titanate electrode material (1.9Na2Ti3O7&Na2Ti7O 15 ).

[0045] The Na2Ti7O prepared in this example 15 Doped Na2Ti3O7 sodium titanate electrode material 1.9Na2Ti3O7&Na2Ti7O 15 The structure of the material was characterized by X-ray diffractometer, and the results are shown in Figure 1. As can be seen from Figure 1, the diffraction peaks of the prepared material are similar to those of Na2Ti3O7 and Na2Ti7O 15 The crystal phase is consistent with that shown in the DFT standard card, indicating that Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate material (1.9Na2Ti3O7&Na2Ti7O 15 ). As can be seen 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 Na2Ti7O 15 The addition of leads to a preferred orientation of the crystal, which increases the exposure of the (100) crystal plane and reduces the exposure of the (003) crystal plane. This increases the diffusion channels of sodium ions and shortens them, which is beneficial to the diffusion and storage of sodium ions.

[0046] The field emission scanning electron microscopy (FE-SEM) was used to analyze the 1.9Na2Ti3O7 & Na2Ti7O 15 The morphology of the material was characterized, and the results are shown in Figure 2. As can be seen from Figure 2, the prepared material is a porous block structure formed by the accumulation of nanorods, and the rod diameter is 100-400nm.

[0047] The 1.9Na2Ti3O7 & Na2Ti7O were characterized by high-angle annular dark-field spherical aberration corrected scanning transmission electron microscopy (HAADF-STEM). 15 The material was characterized, and the results are shown in Figure 3. As can be seen from Figure 3, Na2Ti3O7 regularly appears in the prepared Na2Ti3O7 crystal phase. 15 The crystal phase of Na2Ti7O 15 Successfully doped into Na2Ti3O7 crystal phase. 15 There are 4 TiO6 octahedrons in one structural unit, compared with 3 TiO6 octahedrons in one structural unit of Na2Ti3O7, which has more sodium storage sites and wider sodium ion diffusion channels, thereby improving the specific capacity and rate performance of the material. 15 The upper and lower layers of TiO6 octahedrons are connected to each other, making their structure more stable during the sodium ion insertion / extraction process, thereby increasing the long-cycle stability of the material.

[0048] Example 6:

[0049] This embodiment involves Na2Ti7O 15 The preparation method of the sodium titanate electrode material doped with Na2Ti3O7 comprises the following steps: 1.054g of sodium carbonate and 2.396g of anatase phase titanium dioxide (the molar ratio of sodium carbonate to anatase phase titanium dioxide is 1.99:6) are placed in a high-energy ball mill for 1 hour at room temperature to obtain a uniformly mixed precursor; the precursor is then placed in a microwave tube furnace for high-temperature calcination, specifically: the heating rate is set to 10 degrees Celsius per minute, and the precursor is calcined at 1100 degrees Celsius in an air atmosphere for 20 minutes to obtain Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material (1.99Na2Ti3O7&Na2Ti7O 15 ).

[0050] Comparative Example 1:

[0051] This embodiment relates to a method for preparing a pure phase Na2Ti3O7 sodium titanate electrode material, comprising the following steps: at room temperature, 1.060 g of sodium carbonate and 2.396 g of anatase phase titanium dioxide are placed in a high-energy ball mill for 1 hour to obtain a uniformly mixed precursor; the precursor is then placed in a microwave tube furnace for high-temperature calcination, specifically, the heating rate is set to 10 degrees Celsius per minute, and the mixture is calcined at 850 degrees Celsius in an air atmosphere for 20 minutes to obtain a sodium titanate electrode material (Na2Ti3O7).

[0052] The structure of the Na2Ti3O7 sodium titanate electrode material prepared in this embodiment was characterized by X-ray diffractometer, and the results are shown in Figure 1. As can be seen from Figure 1, the diffraction peaks of the prepared material are consistent with the crystal phase represented by the DFT standard card of Na2Ti3O7, indicating that the pure phase Na2Ti3O7 sodium titanate material was successfully prepared in this embodiment. 15 The electrochemical performance test experiment of doped Na2Ti3O7 sodium titanate electrode material and Na2Ti3O7 sodium titanate electrode material, the specific steps are as follows:

[0053] The Na2Ti7O obtained in Example 1-6 15 The sodium titanate material doped with Na2Ti3O7 and the sodium titanate electrode material obtained in Comparative Example 1 were used as the negative electrode of the sodium ion battery, metallic sodium was used as the counter electrode, glass fiber was used as the diaphragm, sodium perchlorate (NaPF6) was used as the electrolyte, and the Na2Ti7O was packaged in a CR2032 button battery shell in an argon atmosphere glove box to obtain Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material half-cell and Na2Ti3O7 sodium titanate electrode material half-cell. -1) rate, and a voltage range of 0.01-2.5 V. The specific capacities obtained are shown in Table 1. Electrochemical rate performance tests were conducted at rates of 0.1, 0.2, 0.5, 1, 2, 5, 10, and 20 C, and a voltage range of 0.01-2.5 V. The rate performance obtained is shown in Figure 11.

[0054] Table 1 Example 1-6Na2Ti7O 15 The charge capacity (mAh g) of the sodium titanate electrode material doped with Na2Ti3O7 and the sodium titanate electrode material of Comparative Example 1 -1 ).

[0055] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material, characterized in that: Its structure is a porous block structure formed by the accumulation of nanorods with a diameter of 100-400nm.

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 claimed in claim 1 or 2 15 The method of doping Na2Ti3O7 sodium titanate electrode material is characterized in that: The following steps are involved: (1) ball-milling sodium carbonate and anatase phase titanium dioxide to obtain a uniformly mixed precursor mixture; (2) placing the uniformly mixed precursor mixture in a microwave tube furnace and calcining it in an air atmosphere to obtain Na2Ti7O 15 Doped Na2Ti3O7 sodium titanate electrode material.

4. Na2Ti7O according to claim 3 15 The method for preparing a sodium titanate electrode material doped with Na2Ti3O7 is characterized in that: The molar ratio of sodium carbonate: anatase phase titanium dioxide = (1.50-1.99):

6.

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

6. Na2Ti7O as claimed in claim 1 or 2 15 Application of doped Na2Ti3O7 sodium titanate electrode materials in sodium ion batteries.

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