High specific surface area manganese dioxide, and preparation method and application thereof

Abstract

The application discloses high specific surface area manganese dioxide and a preparation method and application thereof, and relates to a preparation method of high specific surface area manganese dioxide, which comprises the following steps: (1) preparing manganese dioxide (MnO2); (2) uniformly mixing the MnO2 obtained in the step (1) with ammonium fluoride (NH4F) according to a mass ratio of 1:3-15, and performing temperature rising and heat preservation in an argon atmosphere; (3) centrifuging, washing and drying the obtained product, and finally collecting the product, so that the high specific surface area manganese dioxide is obtained. The application can control the morphology of the MnO2, improve the specific surface area of the MnO2, and is used for a positive electrode of a magnesium ion capacitor, so that the storage electrochemical performance of the magnesium ion capacitor can be improved.

Description

Technical Field

[0001] This invention relates to positive electrode materials for magnesium ion capacitors, and more particularly to a high specific surface area manganese dioxide, its preparation method, and its applications. Background Technology

[0002] Limited traditional energy sources (such as coal, oil, and natural gas) inevitably produce greenhouse gases like CO2 during use, causing environmental pollution. Therefore, there is a need to develop sustainable, green, environmentally friendly, and pollution-free energy storage technologies. Currently, electrochemical energy storage technology, being environmentally friendly and pollution-free during use, has attracted widespread exploration. Hybrid capacitors, a type of chemical power source, combine the advantages of supercapacitors and batteries and are gaining popularity.

[0003] Positive electrode materials play an irreplaceable role in magnesium-ion capacitors, and actively developing positive electrode materials promotes the development of magnesium-ion capacitors. Among them, MnO2 has a high theoretical specific capacitance (1000 F g). -1 However, the limited specific surface area restricts practical applications, allowing only 1 / 6 of the theoretical capacitance value to be exhibited. Therefore, it is necessary to shape the microstructure of MnO2 to increase the specific surface area, thereby enhancing its charge storage capacity and ultimately improving the specific capacitance of magnesium ion capacitors. Summary of the Invention

[0004] The purpose of this invention is to provide a high specific surface area manganese dioxide, its preparation method, and its application. This method can prepare manganese dioxide with a high specific surface area. When this manganese dioxide is used as the positive electrode material of an aqueous magnesium ion capacitor, the electrochemical performance of the aqueous magnesium ion capacitor can be improved.

[0005] To address the problems existing in the prior art, the technical solution adopted in this invention is:

[0006] In a first aspect, the present invention provides a method for preparing manganese dioxide with a high specific surface area, comprising the following steps:

[0007] (1) Preparation of manganese dioxide (MnO2);

[0008] (2) Using the MnO2 obtained in step (1) as a reaction precursor, it is mixed with ammonium fluoride (NH4F) at a mass ratio of 1:3-15, heated, and kept warm under an argon atmosphere;

[0009] (3) Centrifuge the obtained product, wash and dry it, and finally collect the product to obtain manganese dioxide with high specific surface area.

[0010] Furthermore, the crystal structure of the manganese dioxide (MnO2) is α-MnO2, δ-MnO2, K 1.33 Mn8O16 Or Na 0.55 MnO2.

[0011] Furthermore, both α-MnO2 and δ-MnO2 are synthesized using a hydrothermal method, and the K... 1.33 Mn8O 16 and Na 0.55 MnO2 was prepared by the molten salt method.

[0012] Preferably, the heating rate in step (2) is 2-5℃ / min.

[0013] Furthermore, in step (2), the temperature is maintained at 150℃-300℃ for 0.5-1h.

[0014] Furthermore, in step (3), after washing, the product is dried at 60℃-80℃ for 6h-24h.

[0015] Secondly, the present invention provides a manganese dioxide with a high specific surface area, which is prepared by the preparation method described in the first aspect above.

[0016] Thirdly, the present invention provides the high specific surface area manganese dioxide described in the second aspect above for use in preparing positive electrode materials for aqueous magnesium ion capacitors.

[0017] Fourthly, the present invention provides a magnesium ion capacitor, which is assembled with PTCDI or AC as the negative electrode and manganese dioxide with high specific surface area as the positive electrode as described in the second aspect above.

[0018] The advantages and beneficial effects of this invention are:

[0019] This invention discloses a method for preparing manganese dioxide with high specific surface area. The method involves using manganese dioxide with different crystal structures as precursors, mixing them uniformly with ammonium fluoride in a specific ratio, transferring the mixture to a tube furnace, and allowing it to react fully at a certain temperature. The resulting product is then centrifuged and dried to obtain manganese dioxide with high specific surface area. This method can control the morphology of MnO2 and increase its specific surface area. A higher specific surface area exposes more active sites during contact with the electrolyte, promoting the ability to store charge. This allows for its use as the positive electrode in magnesium-ion capacitors, assembling them with AC or PTCDI as the negative electrode and manganese dioxide as the positive electrode. This process benefits from the morphology of α-MnO2, δ-MnO2, and K+. 1.33 Mn8O 16 and Na 0.55 The unique crystal structure of MnO2, combined with its high specific surface area, works synergistically to enhance the electrochemical performance of aqueous magnesium ion capacitors.

[0020] The high specific surface area manganese dioxide prepared by this invention has broad application prospects in the field of electrochemical energy storage. It can improve specific capacitance, is easy to operate, and has significant practical implications. After reaction with NH4F, the specific surface area of ​​MnO2 is greatly improved, especially that of K. 1.33 Mn8O 16 The specific surface area increased by 6.45 times, reaching 255.5 m². 2 g -1 Na 0.55 The specific surface area of ​​MnO2 increased by 3.51 times, reaching 241.0 m². 2 g -1 The specific surface area of ​​α-MnO2 increased by 4.36 times, reaching 204.5 m². 2 g -1 The specific surface area of ​​δ-MnO2 increased by 15 times, reaching 203.7 m². 2 g -1 Three-electrode electrochemical performance tests show that the aqueous magnesium ion capacitor assembled using manganese dioxide prepared by the method of this invention as the positive electrode has good electrochemical performance, rapid charge-discharge capability, and good cycle stability. Attached Figure Description

[0021] Figure 1 For K 1.33 Mn8O 16 Na 0.55 X-ray diffraction patterns of MnO2, δ-MnO2, β-MnO2, and α-MnO2.

[0022] Figure 2 X-ray diffraction patterns of manganese dioxide with high specific surface area prepared in Examples 1-4 and Comparative Example 1.

[0023] Figure 3 For α-MnO2, β-MnO2, δ-MnO2, Na 0.55 MnO2, K 1.33 Mn8O 16 Scanning electron microscope (SEM) images; in the images: a is α-MnO2, b is β-MnO2, c is δ-MnO2, d is Na 0.55 MnO2 (NMO), e is K 1.33 Mn8O 16 (KMO).

[0024] Figure 4 The images show scanning electron microscope (SEM) images of manganese dioxide with high specific surface area prepared in Examples 1-4 and Comparative Example 1; in the images: a is Example 2, b is Comparative Example 1, c is Example 3, d is Example 4, and e is Example 1.

[0025] Figure 5Transmission electron microscopy (TEM) images of manganese dioxide with high specific surface area prepared in Example 1: In the figures: a is the morphology at 100 nm, b is the morphology at 100 nm, c is the lattice fringes at 10 nm, d is the morphology of HAAD-STEM, e is the mapping of Mn element, f is the mapping of O element, g is the mapping of F element, and h is the mapping of Mn element.

[0026] Figure 6 For α-MnO2, β-MnO2, δ-MnO2, Na 0.55 MnO2, K 1.33 Mn8O 16 Cyclic voltammetry curves and constant current charge-discharge curves: In the figure: a is the CV curve of α-MnO2, a ， b is the CP curve of α-MnO2; b is the CV curve of β-MnO2. ， c is the CP curve of β-MnO2; c is the CV curve of δ-MnO2. ， The CP curve for δ-MnO2 is shown; d represents Na. 0.55 CV curve of MnO2, d ， for Na 0.55 CP curve of MnO2; e is K 1.33 Mn8O 16 The CV curve, e ， For K 1.33 Mn8O 16 The CP curve.

[0027] Figure 7 The figures show the cyclic voltammetry and galvanostatic charge-discharge curves of the high specific surface area manganese dioxide prepared in Examples 1-4 and Comparative Example 1; in the figures:

[0028] a represents the CV curve of Example 2. ， The CP curve for Example 2;

[0029] b is the CV curve of Comparative Example 1, b ， The CP curve for Comparative Example 1;

[0030] c represents the CV curve of Example 3. ， The CP curve for Example 3;

[0031] d represents the CV curve of Example 4. ， The CP curve for Example 4;

[0032] e represents the CV curve of Example 1. ， The CP curve is from Example 1.

[0033] Figure 8Electrochemical performance of magnesium ion capacitors assembled with high specific surface area manganese dioxide prepared in Example 1 and PTCDI: In the figure: a is the CV curve at different scan rates, and b is the CP curve at different current densities.

[0034] Figure 9 Electrochemical performance of magnesium ion capacitors assembled with high specific surface area manganese dioxide prepared in Example 1 and AC: In the figure: a is the CV curve at different scan rates, and b is the CP curve at different current densities. Detailed Implementation

[0035] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. Example 1

[0037] This embodiment provides a method for preparing manganese dioxide with high specific surface area, including the following steps:

[0038] (1) Preparation of K by molten salt method 1.33 Mn8O 16 .

[0039] (2) The K prepared in step (1) 1.33 Mn8O 16 As a reaction precursor, it is mixed evenly with NH4F at a ratio of 1:3, transferred to a tube furnace, the crucible is placed in the center of the tube furnace, argon gas is introduced into the tube furnace, the temperature is increased at a rate of 5℃ / min, and held at 200℃ for 1h.

[0040] The heating rate in step (2) of this application is in the range of 2-5℃ / min, with 5℃ / min being the optimal heating rate. If the heating rate is lower than 2℃ / min, it will affect the efficiency. If the heating rate is higher than 5℃ / min, it will lead to insufficient reaction.

[0041] In step (2) of this application, the temperature range for heat preservation is 150℃-300℃, with 200℃ being the optimal temperature. If the temperature is below 150℃, the chemical reaction will not occur; if the temperature is above 300℃, the synthesis of high specific surface area manganese dioxide will be affected. The heat preservation time ranges from 0.5 to 1 hour, with 1 hour being optimal. If the heat preservation time is less than 0.5 hours, the reaction will be incomplete; if the heat preservation time is longer than 1 hour, the yield will be reduced.

[0042] (3) After the reaction is complete, the product is centrifuged and dried to obtain MnO2 with high specific surface area. Example 2

[0043] This embodiment provides a method for preparing manganese dioxide with high specific surface area. The only difference between this embodiment and Example 1 is that α-MnO2 is prepared by hydrothermal method as a reaction precursor. All other aspects are the same as in Example 1. Example 3

[0044] This embodiment provides a method for preparing manganese dioxide with high specific surface area. The only difference between this embodiment and Example 1 is that δ-MnO2 is prepared by hydrothermal method as a reaction precursor. All other aspects are the same as in Example 1. Example 4

[0045] This embodiment provides a method for preparing manganese dioxide with a high specific surface area. The only difference between this embodiment and Example 1 is that the molten salt method is used to prepare Na. 0.55 MnO2 was used as the reaction precursor, and the rest were the same as in Example 1. Comparative Example 1

[0046] This comparative example provides a method for preparing manganese dioxide with a high specific surface area. The only difference between this comparative example and Example 1 is that β-MnO2 is prepared by hydrothermal method as a reaction precursor. All other aspects are the same as in Example 1.

[0047] Experimental Example 1

[0048] Manganese dioxide K with different crystal structures prepared in step (1) of Examples 1-4 and Comparative Example 1 1.33 Mn8O 16 (KMO), α-MnO2, δ-MnO2, Na 0.55 BET nitrogen adsorption-desorption tests were performed on MnO2 (NMO), β-MnO2, and high specific surface area manganese dioxide prepared in Examples 1-4 and Comparative Example 1 to obtain the specific surface area and pore volume. The test results are shown in Table 1.

[0049] Table 1: Changes in specific surface area and pore volume before and after the reaction of ammonium fluoride

[0050]

[0051] Table 1 shows that, under the same testing conditions, manganese dioxide with different crystal structures all showed an increase in specific surface area to varying degrees after the addition of ammonium fluoride. Among these, the K₂O₂ prepared by the molten salt method showed the greatest increase. 1.33 Mn8O 16 and Na 0.55 MnO2 has the most significant effect on increasing the specific surface area, up to 255.5 m². 2 g -1 The specific surface area of ​​α-MnO2 and δ-MnO2 prepared by hydrothermal method was also significantly increased; although the specific surface area of ​​β-MnO2 prepared by hydrothermal method was also increased, the increase was the smallest compared with other crystal structures.

[0052] like Figure 1 As shown, α-MnO2, β-MnO2, δ-MnO2 prepared by the hydrothermal method, and K2 prepared by the molten salt method can be observed. 1.33 Mn8O 16 and Na 0.55 The MnO2 exhibits distinct diffraction peaks that match the standard XRD pattern, indicating that the prepared MnO2 has good crystallinity and is pure without impurities.

[0053] like Figure 2 As shown, after reacting with ammonium fluoride, the number of diffraction peaks of MnO2 with different crystal structures eventually became two, and the intensity of the diffraction peaks was significantly reduced compared to the original. This indicates that after the reaction, the crystallinity of different phases of manganese dioxide deteriorated and they were transformed into the same substance.

[0054] like Figure 3 As shown, scanning electron microscope (SEM) images of manganese dioxide with different crystal structures at the 200 nm scale clearly show... Figure 3 a is α-MnO2 with a nanorod-like structure and uniform distribution. Figure 3 b represents β-MnO2 with a nanotubular structure. Figure 3 c represents δ-MnO2 in the shape of nanoflower spheres, and the surface of the nanoflower spheres can be clearly seen to be composed of a layered structure. Figure 3 d is Na 0.55 A scanning electron microscope (SEM) schematic diagram of MnO2. Unlike the nanorod structures of α-MnO2 and β-MnO2, it has a nanorod structure on its surface. Figure 3 e represents the K of the nanowire structure. 1.33 Mn8O 16 Compared to α-MnO2 with a nanorod structure, it has a smaller size.

[0055] like Figure 4As shown, scanning electron microscope (SEM) images at a 200 nm scale are obtained after the synthesis of manganese dioxide with different crystal structures using ammonium fluoride. Figure 4 It can be clearly seen that after the reaction of α-MnO2 with ammonium fluoride, the morphology changes from nanorod-like to nanoflower-like. Figure 4 b shows that after the reaction of β-MnO2 with ammonium fluoride, the morphology changes from nanotubes to nanofloral shapes. Figure 4 As shown in Figure c, although the morphology of δ-MnO2 after reacting with ammonium fluoride remains that of nano-flower-like spheres, the size of these spheres becomes smaller after the reaction, which is beneficial for increasing the contact area with the electrolyte. From Figure 4 Na can be seen in d 0.55 After reacting with ammonium fluoride, the morphology of MnO2 changes from nanorod-like to nanoflower-like. From Figure 4 e can see K 1.33 Mn8O 16 After reacting with ammonium fluoride, the nanowire structure transforms into a nanoflower-like structure. In the five reactions... Figure 4 e has the smallest nano-flower-like size and the largest surface area when in contact with the electrolyte.

[0056] like Figure 5 As shown, K 1.33 Mn8O 16 Transmission electron microscopy (TEM) images and elemental distribution maps after the reaction with ammonium fluoride show that manganese dioxide composed of layered nanospheres is clearly visible in Figures a and b. Figure c shows the presence of obvious amorphous regions, consistent with the XRD results. Figure dh shows that Mn, O, F, and K elements are uniformly distributed.

[0057] Experimental Example 1 shows that α-MnO2, δ-MnO2, and K... 1.33 Mn8O 16 and Na 0.55 MnO2 reacted with ammonium fluoride according to the method described in this invention can all obtain MnO2 with high specific surface area. In addition to the crystal structures mentioned above, λ-MnO2, γ-MnO2, ε-MnO2, OMS-6, and todorokite MnO2 crystal structures can all have their specific surface area increased after treatment with ammonium fluoride according to the method described in this invention.

[0058] Experiment Example 2

[0059] 1. Experimental Groups:

[0060] Group 1: K 1.33 Mn8O 16 (KMO);

[0061] Group 2: α-MnO2;

[0062] Group 3: δ-MnO2;

[0063] Group 4: Na 0.55 MnO2 (NMO);

[0064] Group 5: β-MnO2;

[0065] Group 6: High specific surface area manganese dioxide prepared in Example 1;

[0066] Group 7: High specific surface area manganese dioxide prepared in Example 2;

[0067] Group 8: High specific surface area manganese dioxide prepared in Example 3;

[0068] Group 9: High specific surface area manganese dioxide prepared in Example 4;

[0069] Group 10: Manganese dioxide prepared in Comparative Example 1;

[0070] 2. Experimental methods:

[0071] This experiment used a three-electrode system for electrochemical testing on a Chenhua 660e. The working electrode was prepared by mixing manganese dioxide (groups 1-10) with conductive carbon black and polytetrafluoroethylene (PVDF) in a mass ratio of 8:1:1, with an electrode loading of approximately 2 mg / cm³. -2 The prepared electrode sheets were pressed and then dried. The reference electrode was a calomel electrode, and the counter electrode was a graphite rod. At room temperature, the electrolyte solution concentration was 1M, prepared from deionized water and magnesium nitrate, with a pH of approximately 5. Cyclic voltammetry was first performed using different scan rates, with a scan rate of 5 mV / s. -1 10mVs -1 20mVs -1 30mVs -1 40mVs -1 50mVs -1 Then, constant current charge-discharge tests were performed at different current densities. The current density was 0.5 A g. -1 1A g -1 ,3A g -1 5A g -1 10A g -1 15A g -1 20A g -1 The larger the area under the CV curve, the greater the specific capacitance. From... Figures 6 to 7 In the figure, we can see that the area of ​​the CV curve for different crystal forms of manganese dioxide at 1 M mg (NO3)2 increases, indicating that the specific capacitance is improved. Among them, α-MnO2 treated with ammonium fluoride at 0.5 A g -1 At this density, the specific capacitance is 58.55 F g.-1 Upgraded to 416.1F g -1 δ-MnO2, after treatment with ammonium fluoride, at 0.5A g -1 At this density, the specific capacitance is 327.1 F g. -1 Increased to 448.4F g -1 Na 0.55 MnO2 (NMO) treated with ammonium fluoride at 0.5A g -1 At this density, the specific capacitance is 133.3 F g. -1 Increased to 389.6F g -1 β-MnO2, after treatment with ammonium fluoride, at 0.5A g -1 At this density, the specific capacitance is 18.3 F g. -1 Increased to 253.4F g -1 K 1.33 Mn8O 16 After treatment with ammonium fluoride, at 0.5A g -1 At this density, the specific capacitance is 101.8 F g. -1 Increased to 491.5F g -1 The improvement effect is most obvious.

[0072] 3. A magnesium-ion capacitor was assembled using 3,4,9,10-perylenetetracarboxylic acid diimide (PTCDI) as the negative electrode and manganese dioxide with a high specific surface area prepared in Example 1 as the positive electrode. The results are as follows: Figure 8 As shown, in Figure 8 As seen in Figure a, the structure can maintain an approximate rectangular shape at different scan rates, indicating that it has the ability to charge and discharge rapidly. Figure 8 As seen in b, at 0.5A g -1 At a current density of 190.9 F g, the specific capacitance reaches 190.9 F g. -1 It features high specific capacitance and a wide operating voltage window of 2V.

[0073] 4. Using activated carbon (AC) as the negative electrode and manganese dioxide with a high specific surface area prepared in Example 1 as the positive electrode, a magnesium ion capacitor was assembled. The results are as follows: Figure 9 As shown, in Figure 9 As seen in diagram a, the rectangle remains approximately rectangular at different scan rates, indicating its ability to charge and discharge rapidly. Figure 9 As seen in b, the charge-discharge curves always maintain a symmetrical triangular shape under different current densities, especially at 0.5 A g. -1 At a current density of 166.3 Fg, the specific capacitance reaches 166.3 Fg. -1 .

[0074] As can be seen from Experiments 1 and 2, K 1.33 Mn8O 16(KMO), α-MnO2, δ-MnO2, Na 0.55 The specific surface area of ​​MnO2 (NMO) increased significantly after the addition of ammonium fluoride, thanks to K. 1.33 Mn8O 16 (KMO), α-MnO2, δ-MnO2, Na 0.55 The unique crystal structure of MnO2 (NMO) allows for a significant improvement in electrochemical performance by increasing its specific surface area. Among these, K... 1.33 Mn8O 16 The specific surface area increased to 255.5 m² after using ammonium fluoride. 2 g -1 The most significant improvement was in electrochemical performance. Although the specific surface area of ​​β-MnO2 increased after using ammonium fluoride, the improvement was still less pronounced in 1M Mg. 2+ Among the electrolytes, it exhibited the worst electrochemical performance, with only 253.4 F g. -1 .

[0075] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing high specific surface area manganese dioxide for the preparation of aqueous magnesium ion capacitor anode materials, characterized in that, The method comprises the following steps: (1) preparing manganese dioxide (Mn02); the crystal structure of the manganese dioxide (Mn02) is K 1.33 Mn8O 16 or Na 0.55 MnO2; (2) using the manganese dioxide obtained in step (1) as a reaction precursor, mixing uniformly with ammonium fluoride (NH4F) in a mass ratio of 1:3-15, warming, and keeping temperature in an argon atmosphere; (3) centrifuging the obtained product, washing and drying, and finally collecting the product to obtain high specific surface area manganese dioxide.

2. The method for preparing high specific surface area manganese dioxide for preparing aqueous magnesium ion capacitor anode material according to claim 1, characterized in that: The K 1.33 Mn8O 16 and Na 0.55 MnO2were prepared by molten salt method.

3. The method for preparing high specific surface area manganese dioxide for preparing aqueous magnesium ion capacitor anode material according to claim 1, characterized in that: The warming rate in step (2) is 2-5 ℃ / min.

4. The method for preparing high specific surface area manganese dioxide for preparing aqueous magnesium ion capacitor anode material according to claim 1, characterized in that: The temperature keeping in step (2) is 150-300 ℃ for 0.5-1 h.

5. The method for preparing high specific surface area manganese dioxide for preparing aqueous magnesium ion capacitor anode material according to claim 1, characterized in that: The drying in step (3) is carried out at 60-80 ℃ for 6-24 h after washing.

6. A high specific surface area manganese dioxide for the preparation of aqueous magnesium ion capacitor anode material, characterized in that: The high specific surface area manganese dioxide is prepared by the preparation method in any one of claims 1-5.

7. An aqueous magnesium ion capacitor characterized by: The high specific surface area manganese dioxide is used as a positive electrode and assembled with 3,4,9,10-perylenetetracarboxylic diimide or active carbon as a negative electrode.

Images