A method for preparing Al-doped CaTi2O4(OH)2 material by solvothermal method

Abstract

The present invention discloses a method for preparing Al-doped CaTi₂O₄(OH)₂ material by solvothermal method. Step 1: Dissolve anhydrous calcium chloride in dilute nitric acid solution and add anhydrous ethanol and mix. After sealing and magnetic stirring, solution A is obtained; add anhydrous ethanol to tetrabutyl titanate and obtain solution B after sealing and magnetic stirring; Step 2: Slowly drop the B solution prepared in Step 2 into the A solution to obtain a white suspension solution during stirring, and then add aluminum nitrate to obtain solution C; Step 3: Dropwise add NaOH solution to the solution C prepared in Step 2 to adjust its pH value to 8-8.5, and continue stirring to obtain solution D; Step 4: Transfer the solution D prepared in Step 3 into a high-pressure reaction kettle for reaction, and obtain the Al-CaTi₂O₄(OH)₂ composite material after centrifugation, washing and drying. This method has simple process and low cost, and the prepared product has good electrochemical performance, so it has broad market space.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry technology, and particularly to a method for preparing Al-doped CaTi2O4(OH)2 material by solvothermal method. Background Art

[0002] With the continuous strategic adjustment of the energy structure, the proportion of the use of gradually exhausted fossil energy will be gradually reduced in the future, and new clean energies such as wind energy, solar energy, and tidal energy will play an increasingly important role in the world. To solve various problems in new green energy and energy utilization, people's requirements for energy storage devices will also be getting higher and higher. Energy storage devices can be divided into energy type and power type. As a power-type energy storage device, supercapacitor has attracted wide attention due to its advantages such as high power density and long cycle life, and has developed rapidly in recent years. It not only makes up for the low power density of traditional battery devices, but also improves the low energy density of traditional capacitor devices. At the same time, its charge and discharge time is short, and it will not cause serious impact on itself during deep charge and discharge, and can partially or completely replace traditional chemical batteries for high-power and high-energy application scenarios. There are relevant literature reports on the preparation of CaTi2O4(OH)2 single crystal nanosheets, but its disadvantages are small specific capacitance, unstable electrochemical cycling performance, etc.; Dong Weixia et al. doped elements such as Co, Fe, and Ni into CaTi2O4(OH)2 single crystal nanosheets to obtain a sheet structure (ZL201610804282.X), but the electrochemical cycling performance is unstable. Summary of the Invention

[0003] In order to overcome the technical problems of small specific capacitance and unstable electrochemical cycling performance of CaTi2O4(OH)2 single crystal nanosheets, the present invention provides a method for preparing Al-doped CaTi2O4(OH)2 material by solvothermal method, which is low-cost, simple in process and suitable for large-scale production.

[0004] The technical solution of the present invention is: a method for preparing Al-doped CaTi2O4(OH)2 material by solvothermal method, which is characterized by including the following steps:

[0005] Step 1: Dissolve anhydrous calcium chloride in dilute nitric acid solution and add anhydrous ethanol for mixing, and obtain solution A after sealing and magnetic stirring; add anhydrous ethanol to tetrabutyl titanate, and obtain solution B after sealing and magnetic stirring;

[0006] Step 2: Slowly drop the B solution prepared in step 2 into the A solution during stirring to obtain a white suspension solution, and then add aluminum nitrate to obtain solution C;

[0007] Step 3: Dropwise add NaOH solution to the solution C prepared in step 2 to adjust its pH value to 8-8.5, and continue stirring to obtain solution D;

[0008] Step 4: Transfer the solution D prepared in Step 3 into a high-pressure reactor, place the reactor in an oven for hydrothermal reaction. After it cools to room temperature, put the reaction product into a centrifuge tube, discard the supernatant in the upper part of the centrifuge tube after treatment, wash the centrifuged product with distilled water and ethanol respectively until neutral to obtain a white precipitate. Then, grind the white precipitate after freeze-vacuum drying and normal-temperature vacuum drying to obtain the Al-CaTi2O4(OH)2 material;

[0009] In the said Step 1, the molar ratio of tetrabutyl titanate, anhydrous calcium chloride, absolute ethanol and dilute nitric acid is 1:0.91 - 0.97:1.45 - 1.55:1.4 - 1.6;

[0010] In the said Step 2, the addition amount of aluminum is in accordance with the molar ratio Ca:Ti:Al = 1:0.86 - 0.9:0.1 - 0.14;

[0011] In the said Step 3, the addition amount of the NaOH solution is in accordance with the molar ratio tetrabutyl titanate:NaOH = 1:0.9 - 1.1, the concentration of the NaOH solution is 3 mol / L, and the continuous stirring time is 15 - 25 min;

[0012] In the said Step 4, the temperature of the oven is 160 - 200 °C, the hydrothermal reaction time is 22 - 26 h, the centrifugation treatment time is 5 - 7 min, the number of times of washing with distilled water is 5 - 7 times, the number of times of washing with ethanol is 1 - 2 times, the freeze-vacuum drying time is 8 - 12 h, and the normal-temperature vacuum drying time is 8 - 12 h.

[0013] In the said Step 1, the pH of the dilute nitric acid solution is 1 - 3, and the magnetic stirring time is 4 - 6 min.

[0014] In the said Step 4, the inner lining of the high-pressure reactor is polytetrafluoroethylene.

[0015] The Al-CaTi2O4(OH)2 material prepared in the said Step 4 is a curled flaky structure with a length and width of 0.5 - 0.75 μm and a thickness of 0.08 - 0.15 μm. These flaky structures interpenetrate to form a porous structure, and its electrochemical performance is 371 - 376 mAh / g.

[0016] The present invention has the following beneficial effects:

[0017] (1) The present invention uses a one-step solvothermal method to prepare the Al-doped CaTi2O4(OH)2 material. Through acid treatment of the calcium source, its H + is adsorbed on the surface layer of the flaky structure to protect its nano-flaky structure. By introducing Al 3+, enabling it to enter the lattice, broaden the layer spacing, and thus optimize the material structure and its electrochemical performance.

[0018] (2) The present invention utilizes Al 3+ doping has good effects in aspects such as regulating the morphology of the electrode, stabilizing the lamellar structure, and improving conductivity. Firstly, the doping of Al element can play a framework role, making the electrode material structure more stable. In addition, the trivalent aluminum ions have a relatively large polarity, which may distort the lattice of calcium titanate hydroxide, exposing more active sites, thereby improving the electrochemical activity. Compared with pure CaTi2O4(OH)2 nanosheets and other transition metal element ions, the specific capacitance of the material prepared by the present invention is larger and the electrochemical performance is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the cyclic voltammogram of the Al-doped CaTi2O4(OH)2 material prepared in Examples 1-3 of the present invention at a scanning rate of 50 mV / s;

[0020] Figure 2 is the galvanostatic charge-discharge curve of the Al-doped CaTi2O4(OH)2 material prepared in Examples 1-3 of the present invention at a current density of 10 mA / cm 2 ;

[0021] Figure 3 is the AC impedance of the Al-doped CaTi2O4(OH)2 material prepared in Examples 1-3 of the present invention;

[0022] Figure 4 is the cyclic voltammogram of the Al-doped CaTi2O4(OH)2 material prepared in Example 2 of the present invention at different scanning rates;

[0023] Figure 5 is the galvanostatic charge-discharge curve of the Al-doped CaTi2O4(OH)2 material prepared in Example 2 of the present invention at different current densities;

[0024] Figure 6 is the XRD pattern of the Al-doped CaTi2O4(OH)2 material prepared in Examples 1-3 of the present invention;

[0025] Figure 7 is the SEM image of the Al-doped CaTi2O4(OH)2 material prepared by the solvothermal method in Example 3 of the present invention;

[0026] Figure 8 is the Fourier infrared spectrum of the Al-doped CaTi2O4(OH)2 material prepared by the solvothermal method in Examples 1-3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] Step 1: Dissolve 0.01 mol of anhydrous calcium chloride (CaCl2) in 8 ml of dilute nitric acid solution (pH = 1), add 1 ml of anhydrous ethanol and mix. After sealing and magnetic stirring for 4 min, a homogeneous solution A is obtained. Add 4 ml of anhydrous ethanol to 0.097 mol of tetrabutyl titanate (TBOT), and after sealing and magnetic stirring for 4 min, a solution B is obtained. The molar ratio is TBOT:CaCl2:ethanol:nitric acid = 1:0.97:1.55:1.4. The amount of anhydrous ethanol in solution A is based on TBOT:anhydrous ethanol = 1:0.35, and the amount of anhydrous ethanol in solution B is based on TBOT:anhydrous ethanol = 1:1.2.

[0030] Step 2: Slowly add solution B to solution A during stirring to obtain a white suspension solution, then add 0.001 mol of aluminum nitrate to obtain solution C. Gradually add 3 ml of 3 mol / L NaOH solution dropwise to solution C to adjust its pH value to 8. The molar ratio is TBOT:NaOH = 1:0.9. Continue stirring for 15 min to obtain solution D.

[0031] Step 3: Transfer solution D into a polytetrafluoroethylene-lined autoclave, place the autoclave in an oven for hydrothermal reaction, set the temperature to 160 °C and the time to 22 h, and wait for it to cool to room temperature.

[0032] Step 4: Put the reaction product into a centrifuge tube, centrifuge for 5 min, then pour off the supernatant. Wash it 5 times with distilled water and 1 time with ethanol until neutral to obtain a white precipitate. Then freeze-dry the white precipitate for 8 h and vacuum-dry it at room temperature for 8 h to obtain the Al-CaTi2O4(OH)2 (ACT) material.

[0033] Example 2

[0034] Step 1: Dissolve 0.01 mol of anhydrous calcium chloride (CaCl2) in dilute nitric acid solution (pH = 2), add 1 ml of anhydrous ethanol and mix. After sealing and magnetic stirring for 5 min, a homogeneous solution A is obtained. Add 5 ml of anhydrous ethanol to 0.091 mol of tetrabutyl titanate (TBOT), and after sealing and magnetic stirring for 5 min, a solution B is obtained. The molar ratio is TBOT:CaCl2:ethanol:nitric acid = 1:0.91:1.5:1.5. The amount of anhydrous ethanol in solution A is based on TBOT:anhydrous ethanol = 1:0.55, and the amount of anhydrous ethanol in solution B is based on TBOT:anhydrous ethanol = 1:0.95.

[0035] Step 2: Slowly add solution B dropwise to solution A while stirring to obtain a white suspension solution, then add 0.0012 mol of aluminum nitrate to obtain solution C. Gradually add 3.2 ml of 3 mol / L NaOH solution to solution C to adjust its pH value to 8.5. According to the molar ratio of TBOT:NaOH = 1:1, continue stirring for 20 min to obtain solution D;

[0036] Step 3: Transfer solution D into a polytetrafluoroethylene-lined autoclave, place the autoclave in an oven for hydrothermal reaction, set its temperature to 180 °C and time to 24 h, and wait for it to cool to room temperature;

[0037] Step 4: Put the reaction product into a centrifuge tube, centrifuge for 6 min, then pour off the supernatant. Wash it 6 times with distilled water and 1 time with ethanol until neutral to obtain a white precipitate. Then freeze-dry the white precipitate for 10 h and vacuum-dry it at room temperature for 10 h to obtain the Al-CaTi2O4(OH)2 (ACT) material.

[0038] Example 3

[0039] Step 1: Dissolve 0.01 mol of anhydrous calcium chloride (CaCl2) in a dilute nitric acid solution (pH = 3) and add 1 ml of anhydrous ethanol and mix. After sealing and magnetic stirring for 6 min, a uniform solution A is obtained. Add 6 ml of anhydrous ethanol to 0.092 mol of tetrabutyl orthotitanate (TBOT). After sealing and magnetic stirring for 6 min, solution B is obtained. According to the molar ratio of TBOT:CaCl2:ethanol:nitric acid = 1:0.92:1.45:1.6, the amount of anhydrous ethanol in solution A is based on TBOT:anhydrous ethanol = 1:0.55, and the amount of anhydrous ethanol in solution B is based on TBOT:anhydrous ethanol = 1:0.9;

[0040] Step 2: Slowly add solution B dropwise to solution A while stirring to obtain a white suspension solution, then add 0.0014 mol of aluminum nitrate to obtain solution C. Gradually add 3.5 ml of 3 mol / L NaOH solution to solution C to adjust its pH value to 8.2. According to the molar ratio of TBOT:NaOH = 1:1.1, continue stirring for 25 min to obtain solution D;

[0041] Step 3: Transfer solution D into a polytetrafluoroethylene-lined autoclave, place the autoclave in an oven for hydrothermal reaction, set its temperature to 200 °C and time to 26 h, and wait for it to cool to room temperature.

[0042] Step 4: Put the reaction product into a centrifuge tube, centrifuge for 7 min, then pour off the supernatant. Wash it 7 times with distilled water and 2 times with ethanol until neutral to obtain a white precipitate. Then freeze-dry the white precipitate for 12 h and vacuum-dry it for 12 h to obtain the Al-CaTi2O4(OH)2 (ACT) material.

[0043] To further investigate the electrochemical properties of the material, electrodes were prepared and subjected to cyclic voltammetry, constant current charge-discharge, and AC impedance tests using a three-electrode system on an electrochemical workstation. A 6 mol / L KOH solution was used as the electrolyte, the charge-discharge voltage window was 0-0.7 V, the scan rate of the CV curve was 10 mV / s, and the constant current charge-discharge current density was uniformly set at 10 mA / cm 2 This facilitates comparison of capacitor performance.

[0044] from Figure 1 It can be seen that the CV curves of the three examples all have a pair of obvious redox peaks, which are caused by the redox reaction of Ti. Compared with the pure CaTi2O4(OH)2 example, they have a larger area, thus having better electrochemical performance.

[0045] from Figure 2 As can be seen from the diagram, the GCD curves of the three examples are essentially similar in shape. The longest charge-discharge time indicates the highest specific capacitance and superior electrochemical performance. This is calculated using the single-electrode specific capacitance formula: Cs = I∆t / 3.6m. Here, Cs (mAh / g) represents the specific capacity of the electrode, I (A) is the discharge current, ∆t (s) is the discharge time, and m (g) represents the mass of active material in the electrode. Based on the electrochemical formula, the specific capacities of Examples 1, 2, and 3 were calculated to be 371 mAh / g, 376 mAh / g, and 372 mAh / g, respectively.

[0046] from Figure 3 It can be seen that the oblique lines of each curve of the three embodiments have a large inclination angle in the low-frequency region, indicating that the diffusion performance of the electrode is good. The materials of the three embodiments basically do not have obvious semicircular arcs in the high-frequency region, which means that the charge transfer impedance (Rct) of the electrode is small. It can be seen from the high-frequency region that the radius of the material of the embodiment is significantly smaller than that of pure CaTi2O4(OH)2, so it has better conductivity, and has a smaller charge transfer impedance in the low-frequency region, so its AC impedance is small and its electrochemical performance is excellent.

[0047] from Figures 4-5 As can be seen from the graph, the material of Example 2 maintains a clear redox peak and a high degree of symmetry at each scan rate. Furthermore, as the scan rate increases, the peak current value of the redox peak also increases, but the potential of the redox peak remains essentially unchanged, indicating that the material electrode has a high degree of redox reversibility and good rate performance. The charge and discharge time decreases with increasing current density, which may be attributed to the fact that the electron and ion exchange rate is too fast, preventing them from entering the interior of the electrode material to react, resulting in a reduced utilization of the active material and a reduced specific capacitance.

[0048] fromFigure 6 It can be seen that with the increase of the doping amount of Al in the three embodiments, the characteristic diffraction peaks of the CaTi2O4(OH)2 material gradually increase. This is because with the increase of the aluminum content, the crystallization performance of the CaTi2O4(OH)2 material increases, resulting in the enhancement of the characteristic peaks shown on the XRD.

[0049] As can be seen from Figure 7 the embodiment 3 material has a curled sheet structure with a length and width of 0.5 - 0.75 μm and a thickness of 0.08 - 0.15 μm. These sheet structures interpenetrate to form a porous structure, which is beneficial to the transmission and exchange of electrolyte ions.

[0050] As can be seen from Figure 8 the three embodiment materials have an absorption band at a wavelength of 3391.01 cm -1 corresponding to the stretching vibration of the OH- bond in the layer. Compared with the free state OH- (3600 cm -1 ), the wavelength shifts to a lower wavenumber because there is a hydrogen bond interaction between the interlayer H2O and the layer board OH- or the interlayer CO3 2- . The absorption band centered at 1537.01 cm -1 is caused by the H-O-H bending vibration of the lattice water, which is mainly due to the adsorption of water on the material surface and the insertion of a certain amount of H2O in the interlayer voids. The absorption peak below 500 cm -1 with a central absorption band at 495.62 cm -1 corresponds to the bending vibration of Ca-Ti-O.

[0051] The above embodiments only exemplarily illustrate the principles and effects of the present invention and some applied embodiments, rather than limiting the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for preparing Al-doped CaTi2O4(OH)2 material by solvothermal method, characterized in that It includes the following steps: Step 1: Dissolve anhydrous calcium chloride in dilute nitric acid solution, add anhydrous ethanol and mix. After sealing and magnetic stirring, solution A is obtained; add anhydrous ethanol to tetrabutyl titanate, and obtain solution B after sealing and magnetic stirring; Step 2: Slowly drop the B solution prepared in Step 2 into the A solution during stirring to obtain a white suspension solution, and then add aluminum nitrate to obtain solution C; Step 3: Dropwise add NaOH solution to the solution C prepared in Step 2 to adjust its pH value to 8 - 8.5, and continue stirring to obtain solution D; Step 4: Transfer the solution D prepared in Step 3 into a high-pressure reactor, place the reactor in an oven for hydrothermal reaction. After it cools to room temperature, put the reaction product into a centrifuge tube for treatment, pour out the upper clear liquid in the centrifuge tube, wash the centrifuged product with distilled water and ethanol respectively until neutral to obtain a white precipitate. Then, grind the white precipitate after freeze-vacuum drying and normal-temperature vacuum drying to obtain the Al-CaTi2O4(OH)2 material; In Step 1, the molar ratio of tetrabutyl titanate to anhydrous calcium chloride to anhydrous ethanol to dilute nitric acid is 1:0.91 - 0.97:1.45 - 1.55:1.4 - 1.6; In Step 2, the addition amount of aluminum is in accordance with the molar ratio Ca:Ti:Al = 1:0.86 - 0.9:0.1 - 0.14; In Step 3, the addition amount of NaOH solution is in accordance with the molar ratio tetrabutyl titanate:NaOH = 1:0.9 - 1.1, the concentration of the NaOH solution is 3 mol / L, and the time for continuous stirring is 15 - 25 min; In Step 4, the temperature of the oven is 160 - 200 °C, the time for hydrothermal reaction is 22 - 26 h, the time for centrifugation is 5 - 7 min, the number of times of washing with distilled water is 5 - 7 times, the number of times of washing with ethanol is 1 - 2 times, the time for freeze-vacuum drying is 8 - 12 h, and the time for normal-temperature vacuum drying is 8 - 12 h.

2. The method according to claim 1, characterized in that: In Step 1, the pH of the dilute nitric acid solution is 1 - 3, and the time for magnetic stirring is 4 - 6 min.

3. The method according to claim 1, wherein: In Step 4, the inner lining of the high-pressure reactor is polytetrafluoroethylene.

4. The method according to claim 1, wherein: The Al-CaTi2O4(OH)2 material prepared in Step 4 is a curled sheet structure with a length dimension of 0.5 - 0.75 μm, a width dimension of 0.5 - 0.75 μm, and a thickness of 0.08 - 0.15 μm. These sheet structures interpenetrate to form a porous structure, and its specific capacity is 371 - 376 mAh / g.

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