Preparation method of a three-dimensional Mn-CoLDH / MnCo2O4 nanocomposite

Abstract

The present invention relates to a method for preparing a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite, belonging to the field of novel energy storage materials. The method comprises the following steps: Dissolve 0.75 to 1.5 mmol of MnCl2·4H2O, 1.5 to 4.5 mmol of Co(NO3)2·6H2O, 4.5 mmol of urea and 3.75 mmol of NH4F in 30 ml of deionized water, and obtain a homogeneous reaction solution after magnetic stirring for 15 min; Transfer the reaction solution into a 50-ml reaction kettle, immerse the nickel foam grown with MnCo2O4 into the solution, seal the reaction kettle and heat it at 120 °C for 6 to 12 h, and after the reaction is completed, wash and dry the sample to obtain the three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite. The method for preparing the Mn-Co LDH / MnCo2O4 nanocomposite is relatively simple, and the electrochemical energy storage performance of the sample is outstanding, which is not only beneficial to broadening the application of the Mn-Co LDH / MnCo2O4 nanocomposite in electrochemical energy storage devices such as supercapacitors, but also provides a new way for designing novel energy materials.

Description

Technical Field

[0001] The present invention relates to a preparation method of a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite material, which can be used for electrochemical energy storage and belongs to the field of new energy storage materials. Background Art

[0002] In recent years, the development of sustainable storage and conversion devices to solve the global energy shortage problem has attracted extensive attention. Supercapacitors have received increasing attention due to their high power density, low cost, fast charge and discharge process, long cycle time and other advantages. In the structure of supercapacitors, the electrode material determines the performance of supercapacitors. Therefore, the development of high-performance electrochemical electrode materials is crucial.

[0003] Bimetallic oxides (such as FeCo2O4, NiCo2O4, CoMn2O4 and MnFe2O4, etc.) have been widely studied as electrode materials for energy storage devices. As electrode materials, different from single metal oxides, due to the complementarity and synergistic effect of the properties of the two metals, bimetallic oxides exhibit excellent electrochemical performance in terms of capacitance, conductivity and structural stability. MnCo2O4 is a typical bimetallic oxide with a spinel structure. As a supercapacitor electrode material, it can provide more active sites for electrochemical energy storage reactions and is a good electrochemical energy storage material.

[0004] Mn-Co LDH is a bimetallic hydroxide, generally in a flaky structure. This structure can expose more active sites in electrochemical reactions and can also fully contact the electrolyte, enabling more ions to participate in the exchange and improving the speed of electrochemical reactions. Using Mn-Co LDH as the electrode material of a supercapacitor can obtain a higher specific capacitance and energy density.

[0005] Combining Mn-Co LDH with the spinel structure MnCo2O4 material to construct a Mn-Co LDH / MnCo2O4 nanocomposite material for use as the electrode material of a supercapacitor can make full use of the synergistic effect of Mn-Co LDH and MnCo2O4, give play to the advantages of the two as electrode materials, further improve the performance of supercapacitors such as specific capacitance, energy density and power density, promote the development of supercapacitor technology, and broaden the application of supercapacitors in fields such as memory, computer and automobile. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that the electrode materials of supercapacitors have problems such as low specific capacitance and low energy density. The object of the present invention is to provide a preparation method of a three-dimensional Mn-CoLDH / MnCo2O4 nanocomposite with high specific capacitance and energy density. This nanocomposite is used as the electrode material of a supercapacitor and exhibits excellent electrochemical energy storage performance.

[0007] The technical solution of the present invention:

[0008] A preparation method of a three-dimensional Mn-CoLDH / MnCo2O4 nanocomposite, comprising the following steps:

[0009] (1) Measure 30 ml of deionized water and pour it into a beaker. Add 1.5 mmol of MnCl2·4H2O, 3 mmol of CoCl2·6H2O, 3 mmol of NH4F, and 6.75 mmol of urea, and stir magnetically for 20 - 40 min; pour the uniformly mixed solution into a 50 ml reaction kettle, use forceps to pick up nickel foam and put it in, and heat at a temperature of 130 - 150 °C for 8 - 12 h; after the reaction is completed, wash and dry the sample to obtain a MnCo2O4 / Ni matrix.

[0010] (2) Dissolve 0.75 - 1.5 mmol of MnCl2·4H2O, 1.5 - 4.5 mmol of Co(NO3)2·6H2O, 4.5 mmol of urea, and 3.75 mmol of NH4F in 30 ml of deionized water, and stir magnetically for 10 - 20 min to obtain a uniform reaction solution.

[0011] (3) Transfer the reaction solution to a 50 ml reaction kettle, immerse the MnCo2O4 / Ni matrix in the reaction solution, heat at 110 - 130 °C for 6 - 12 h, after the reaction is completed, take out the sample, wash and dry it to obtain a three-dimensional Mn-CoLDH / MnCo2O4 nanocomposite.

[0012] In the described preparation method, the three-dimensional Mn-CoLDH / MnCo2O4 nanocomposite is used as the electrode material of a supercapacitor, and an aqueous KOH solution with a molar concentration of 5 - 7 M is used as the electrolyte, and its electrochemical energy storage performance is tested in a three-electrode system and a two-electrode system respectively.

[0013] In the described preparation method, the three-dimensional Mn-CoLDH / MnCo2O4 nanocomposite and activated carbon are used as the positive and negative electrodes respectively to assemble a solid-state supercapacitor, and its electrochemical energy storage performance is tested in a two-electrode system respectively.

[0014] In the described preparation method, in step (1), the reacted sample is dried at 60 - 70 °C for 16 h.

[0015] In the preparation method described above, in step (2), after MnCl2·4H2O, Co(NO3)2·6H2O, urea and NH4F are dissolved, the solution is the solution of the Mn-Co LDH nanomaterial.

[0016] In the preparation method described above, in step (3), the reacted sample is dried at 65 °C for 16 h.

[0017] The technical concept of the present invention is as follows: Both Mn-Co LDH (LDH refers to layered double hydroxide) and MnCo2O4 have good electrochemical energy storage performance. Preparing the two on nickel foam to construct a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite is conducive to making full use of the electrochemical properties of the two. By optimizing the process parameters for material growth, optimizing the structure of the Mn-Co LDH / MnCo2O4 nanocomposite, regulating its interface, and improving its electrochemical energy storage performance. In addition, Mn-Co LDH is a flaky structure material, which is conducive to exposing more active sites and fully contacting with the electrolyte in the electrochemical reaction, exchanging more ions, and increasing the speed of the electrochemical reaction and the specific capacitance and energy density of the electrochemical energy storage. The MnCo2O4 material is a typical spinel structure, with Mn and Co being +2 and +3 valence respectively, which can enrich the active sites of the electrochemical reaction and has good electrochemical energy storage performance. The nanocomposite grows directly on three-dimensional nickel foam. Nickel foam has good conductivity, reduces the resistance between the composite material and the substrate, improves the electrochemical performance, and nickel foam has a three-dimensional porous structure, which is conducive to the migration of the electrolyte. In short, the present invention uses a simple hydrothermal method + heat treatment method to construct a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite and uses it as the electrode material of a supercapacitor, showing its excellent electrochemical energy storage, obtaining a high specific capacitance and energy density, indicating its good application prospect in the field of energy storage.

[0018] The principle of the present invention is as follows: The MnCo2O4 material is a spinel structure material, which can provide rich active sites for the electrochemical reaction, increasing the speed and Coulomb efficiency of the chemical reaction for electrochemical energy storage. Mn-Co LDH has a flaky structure and has a large surface area for the electrochemical energy storage reaction, can contact well with the electrolyte, and promotes the progress of the electrochemical energy storage reaction. Growing it on the MnCo2O4 / Ni substrate to construct a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite can give full play to the respective advantages of Mn-Co LDH and MnCo2O4 in electrochemical energy storage, significantly increasing the specific capacitance and energy density of the nanocomposite, thus obtaining a high-performance three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite.

[0019] The biggest feature of the present invention is: a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite is prepared by using a simple hydrothermal + heat treatment method. First, a uniform reaction solution is prepared from MnCl2·4H2O, CoCl2·6H2O, NH4F and urea. Through hydrothermal reaction + heat treatment, MnCo2O4 nanomaterials are prepared on nickel foam as the matrix of the nanocomposite. Then, Mn-Co LDH is prepared on the MnCo2O4 / Ni matrix through hydrothermal reaction to obtain the Mn-Co LDH / MnCo2O4 nanocomposite. Finally, it is used as the electrode material of a supercapacitor, and the electrochemical energy storage performance of the Mn-Co LDH / MnCo2O4 nanocomposite is comprehensively analyzed in liquid and solid supercapacitors respectively. Its preparation process is simple and the cost is low, which is conducive to the wide application of the material.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] 1. The present invention makes full use of the electrochemical energy storage performance of Mn-Co LDH and MnCo2O4, combines the two, constructs a three-dimensional nanocomposite on nickel foam, and uses it as the electrode material of a supercapacitor. The electrochemical energy storage performance of the three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite is studied by respectively assembling liquid and solid supercapacitor systems. The present invention provides a method for constructing a three-dimensional nanocomposite, which can promote the development of supercapacitor technology.

[0022] 2. The present invention prepares a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite with outstanding electrochemical energy storage performance by using a simple hydrothermal + heat treatment method. This method not only helps to improve the specific capacitance and energy density of the supercapacitor, but also will promote the application of the Mn-Co LDH / MnCo2O4 nanocomposite in fields such as memory, computer, and automobile. Description of the Drawings

[0023] Figure 1 . XRD patterns of MnCo2O4, Mn-Co LDH and Mn-Co LDH / MnCo2O4 nanomaterials in typical embodiments: (a) MnCo2O4; (b) Mn-Co LDH; (c) Mn-Co LDH / MnCo2O4; the abscissa 2θ represents the diffraction angle (°), and the ordinate Intensity represents the relative intensity (a.u.).

[0024] Figure 2Typical SEM images of the Mn-CoLDH / MnCo2O4 nanocomposite in a typical embodiment; among them: the magnification factors from left to right in the first row are ×300, ×1000, and ×2000 respectively, and the magnification factors from left to right in the second row are ×5000, ×5000, and ×5000 respectively.

[0025] Figure 3 EDS diagram of the Mn-CoLDH / MnCo2O4 nanocomposite in a typical embodiment: (a) SEM image of the EDS scanning area; (b) EDS spectrum; (c) EDS element distribution diagram, where the abscissa Energy represents energy (keV) and the ordinate Intensity represents relative intensity (a.u.); (O) is the O element distribution diagram; (Mn) is the Mn element distribution diagram; (Co) is the Co element distribution diagram.

[0026] Figure 4 Electrochemical performance curves of the MnCo2O4 (MCO), Mn-CoLDH (LDH), and Mn-CoLDH / MnCo2O4 (10h, i.e., M-10) nanomaterials in a typical embodiment: (a) CV curve, where the abscissa Potential represents potential (V) and the ordinate Current represents current (A); (b) charge-discharge curve, where the abscissa Time represents time (sec) and the ordinate Potential represents potential (V); (c) specific capacitance histogram, where the ordinate Areal capacity represents specific capacitance (mF / cm 2 ); (d) impedance diagram, and the inset in it is an enlarged view of the impedance between 0 and 1.5 Ω, where the abscissa Z′ represents the real part of the impedance (Ohm) and the ordinate -Z″ represents the imaginary part of the impedance (Ohm).

[0027] Figure 5.Electrochemical performance of the Mn-CoLDH / MnCo2O4 / / C two-electrode supercapacitor with 6M KOH electrolyte in a typical embodiment: (a) Cyclic voltammetry (CV) curves of the C electrode and the nanocomposite in a three-electrode system. The abscissa Potential represents the potential (V), and the ordinate Current represents the current (A); (b) CV curves at different voltage windows. The abscissa Potential represents the potential (V), and the ordinate Current represents the current (A); (c) CV curves at different scan rates. The abscissa Potential represents the potential (V), and the ordinate Current represents the current (A); (d) Charge-discharge curves at different voltage windows. The abscissa Time represents the time (sec), and the ordinate Potential represents the potential (V); (e) Charge-discharge curves at different current densities. The abscissa Time represents the time (sec), and the ordinate Potential represents the potential (V); (f) Impedance curve. The abscissa Z′ represents the real part of the impedance (Ohm), and the ordinate -Z″ represents the imaginary part of the impedance (Ohm).

[0028] Figure 6 .Electrochemical performance of the solid-state electrolyte Mn-CoLDH / MnCo2O4 / / C two-electrode supercapacitor in a typical embodiment: (a) CV curves at different voltage windows. The abscissa Potential represents the potential (V), and the ordinate Current represents the current (A); (b) Charge-discharge curves at different voltage windows. The abscissa Time represents the time (s), and the ordinate Potential represents the potential (V); (c) Charge-discharge curves at different current densities. The abscissa Time represents the time (s), and the ordinate Potential represents the potential (V). Detailed implementation manners

[0029] Next, the present invention will be further described in conjunction with embodiments.

[0030] Typical embodiment

[0031] In this embodiment, a preparation method of a three-dimensional Mn-CoLDH / MnCo2O4 nanocomposite includes the following steps:

[0032] (1) Measure 30 ml of deionized water and pour it into a beaker. Add 1.5 mmol of MnCl2·4H2O, 3 mmol of CoCl2·6H2O, 3 mmol of NH4F, and 6.75 mmol of urea, and stir magnetically for 30 min. Pour the uniformly mixed solution into a 50-ml reaction kettle, use tweezers to pick up nickel foam and put it in, and heat at 140 °C for 10 h. After the reaction is completed, wash and dry the sample (65 °C, 16 h) to obtain the MnCo2O4 / Ni substrate;

[0033] (2) Dissolve 1.0 mmol of MnCl2·4H2O, 3.0 mmol of Co(NO3)2·6H2O, 4.5 mmol of urea and 3.75 mmol of NH4F in 30 ml of deionized water, and obtain a homogeneous reaction solution after magnetic stirring for 15 min;

[0034] (3) Transfer the reaction solution to a 50 ml reaction kettle, immerse the MnCo2O4 / Ni substrate into the reaction solution, heat it at 120 °C for 10 h. After the reaction is completed, take out the sample, wash and dry it (65 °C, 16 h) to obtain a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite;

[0035] (4) Use the three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite as the electrode material of the supercapacitor, and use an aqueous KOH solution with a molar concentration of 6 M as the electrolyte to test its electrochemical energy storage performance in a three-electrode system and a two-electrode system respectively;

[0036] (5) Assemble the Mn-Co LDH / MnCo2O4 nanocomposite and activated carbon as the positive and negative electrodes into a solid-state supercapacitor, and use a two-electrode system to test its electrochemical energy storage performance respectively.

[0037] The structure and electrochemical performance of the samples prepared by the above typical implementation process show that:

[0038] As Figure 1 shown, the XRD patterns of the typical examples of MnCo2O4, Mn-Co LDH and Mn-Co LDH / MnCo2O4 nanomaterials: (a) MnCo2O4; (b) Mn-Co LDH; (c) Mn-Co LDH / MnCo2O4. It can be seen from Figure 1 the XRD images that: in the XRD pattern of MnCo2O4, the diffraction peaks corresponding to its (220), (311), (511) and (440) crystal planes appear ( Figure 1 a); in the XRD pattern of Mn-Co LDH, the positions of its diffraction peaks are also consistent with the literature reports ( Figure 1 b); in the Mn-Co LDH / MnCo2O4 nanocomposite, stronger peaks of MnCo2O4 and weaker peaks of Mn-Co LDH can be seen, indicating that the two materials are successfully compounded ( Figure 1 c).

[0039] As Figure 2As shown, SEM images of the Mn-CoLDH / MnCo2O4 nanocomposite at typical different magnifications in the typical embodiment. It can be seen from the figure that MnCo2O4 is a microsphere composed of nanoneedles, and the Mn-CoLDH nanosheets are embedded between the nanoneedles. Such a structure endows the nanocomposite with a large specific surface area, which is beneficial to contact with the electrolyte and improve its electrochemical energy storage performance.

[0040] As Figure 3 shown, the EDS diagram of the Mn-CoLDH / MnCo2O4 nanocomposite in the typical embodiment. It can be seen from the figure the EDS spectra corresponding to the three elements of Mn, Co, and O, and the distribution of the three elements is relatively uniform.

[0041] As Figure 4 shown, the electrochemical performance graphs of the MnCo2O4 (MCO), Mn-CoLDH (LDH), and Mn-CoLDH / MnCo2O4 (10h) nanomaterials in the typical embodiment: (a) CV curve; (b) charge-discharge curve; (c) specific capacitance bar graph; (d) impedance graph. From Figure 4 a, it can be seen that under the same test conditions, the Mn-CoLDH / MnCo2O4 nanocomposite has a larger CV area and a longer charge-discharge time, indicating that the nanocomposite has a higher specific capacitance. According to Figure 4 the calculation in b, the specific capacitances of MnCo2O4 (MCO), Mn-CoLDH (LDH), and Mn-CoLDH / MnCo2O4 (10h) are 1490, 1410, and 7700 mF cm -2 ， respectively. The capacitance of the composite material is 5 times that of the individual materials before compounding; from Figure 4 c, it can be seen that after the two materials are compounded, at the same current density, the charge-discharge performance of M-10 is significantly enhanced and has a larger specific capacitance value. Moreover, as Figure 4 shown in the impedance graph of d, the nanocomposite also exhibits a smaller resistance, which is beneficial to the transfer of electrons and ions.

[0042] As Figure 5 shown, the electrochemical performance of the Mn-CoLDH / MnCo2O4 / / C two-electrode supercapacitor with 6M KOH electrolyte in the typical embodiment: (a) CV curves of the C electrode and the nanocomposite with three electrodes; (b) CV curves at different voltage windows; (c) CV curves at different scanning speeds: (d) charge-discharge curves at different voltage windows; (e) charge-discharge curves at different current densities; (f) impedance curves. From Figure 5From the cyclic voltammetry (CV) curves of the C electrode and the Mn-CoLDH / MnCo2O4 three-electrode, it can be seen that the C electrode exhibits the characteristics of electric double-layer capacitance while the nanocomposite exhibits pseudocapacitance characteristics. The assembled two-electrode capacitor shows good electrochemical energy storage performance. Its CV curves ( Figure 5 b, Figure 5 c) and charge-discharge curves ( Figure 5 d, Figure 5 e) all show typical pseudocapacitance characteristics and have a relatively high specific capacitance. From Figure 5 f, it can be seen that the impedance of the sample under two-electrode testing is approximately 1.75 Ω, indicating that the internal resistance of this material is very small and it has good electrical conductivity.

[0043] As Figure 6 shown, the electrochemical performance of the solid-state electrolyte Mn-CoLDH / MnCo2O4 / / C two-electrode supercapacitor in a typical embodiment: (a) CV curves at different voltage windows; (b) charge-discharge curves at different voltage windows; (c) charge-discharge curves at different current densities. The solid-state capacitor assembled with the C electrode and Mn-CoLDH / MnCo2O4 shows good electrochemical energy storage performance. Its CV curves ( Figure 6 a) and charge-discharge curves ( Figure 6 b, Figure 6 c) all show typical pseudocapacitance characteristics and have a relatively high specific capacitance.

[0044] The implementation results show that the method for preparing the Mn-CoLDH / MnCo2O4 nanocomposite by the present invention is relatively simple, and the sample has outstanding electrochemical energy storage performance, which is not only conducive to broadening the application of the Mn-CoLDH / MnCo2O4 nanocomposite in electrochemical energy storage devices such as supercapacitors, but also provides a new way for the design of new energy materials.

Claims

1. A preparation method of a three-dimensional Mn-CoLDH / MnCo2O4 nanocomposite, characterized in that, It includes the following steps: (1) Measure 30 ml of deionized water and pour it into a beaker. Add 1.5 mmol of MnCl2·4H2O, 3 mmol of CoCl2·6H2O, 3 mmol of NH4F, and 6.75 mmol of urea, and stir magnetically for 30 min. Pour the well-mixed solution into a 50-ml reaction kettle, use tweezers to pick up nickel foam and put it in, and heat it at 140 °C for 10 h. After the reaction is completed, wash and dry the sample to obtain the MnCo2O4 / Ni substrate; (2) Dissolve 1.0 mmol of MnCl2·4H2O, 3.0 mmol of Co(NO3)2·6H2O, 4.5 mmol of urea, and 3.75 mmol of NH4F in 30 ml of deionized water, and obtain a homogeneous reaction solution after magnetic stirring for 15 min; (3) Transfer the reaction solution to a 50-ml reaction kettle, immerse the MnCo2O4 / Ni substrate into the reaction solution, heat it at 120 °C for 10 h. After the reaction is completed, take out the sample, wash and dry it to obtain a three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite. MnCo2O4 is a microsphere composed of nanoneedles, and Mn-Co LDH nanosheets are embedded between the nanoneedles; Use the three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite as the electrode material of the supercapacitor, and use an aqueous KOH solution with a molar concentration of 6 M as the electrolyte to test its electrochemical energy storage performance in a three-electrode system and a two-electrode system respectively.

2. The preparation method according to claim 1, characterized in that, Use the three-dimensional Mn-Co LDH / MnCo2O4 nanocomposite and activated carbon as the positive and negative electrodes respectively to assemble a solid-state supercapacitor, and test its electrochemical energy storage performance in a two-electrode system respectively.

3. The preparation method according to claim 1, characterized in that, In step (1), dry the reacted sample at 60-70 °C for 16 h.

4. The preparation method according to claim 1, wherein In step (2), the solution after dissolving MnCl2·4H2O, Co(NO3)2·6H2O, urea, and NH4F is the solution of the Mn-Co LDH nanomaterial.

5. The preparation method according to claim 1, characterized in that, In step (3), dry the reacted sample at 65 °C for 16 h.

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