Preparation method of hollow carbon sphere-coated manganese dioxide composite material

Abstract

This scheme discloses a method for preparing a hollow carbon ball coated manganese dioxide composite material in the field of supercapacitors. The method firstly mixes ammonia water, ethanol, pure water and tetraethyl orthosilicate, then adds dopamine hydrochloride, and obtains silicon balls after reaction and drying; then the silicon balls are sintered under high temperature nitrogen protection conditions, and hollow carbon balls are obtained by soaking in hydrofluoric acid; finally, the hollow carbon balls are added to potassium permanganate aqueous solution for reaction, and the preparation of hollow carbon ball coated manganese dioxide material is completed after drying. The material has a hollow structure and a stable and uniform shape, which is conducive to ion diffusion and increases the reactive surface area of ​​the electrode material. The composite material has good capacitance characteristics at different rates, which has a positive effect on the improvement of the capacitance characteristics of supercapacitors. The composite material prepared by this method has excellent electrochemical activity and stable performance, and can be applied to the field of high-capacity supercapacitors.

Description

Technical Field

[0001] The invention belongs to the field of supercapacitors, and particularly relates to a method for preparing a hollow carbon sphere-coated manganese dioxide composite material. Background Art

[0002] As human society's demand for renewable energy becomes increasingly urgent, scientific researchers are increasingly conducting research on energy storage technology. The two most representative energy storage devices today are lithium-ion batteries (LIBS) and supercapacitors (SCS). LIBS is based on the principle of redox reactions in electrode materials to store and release energy. This mechanism can obtain higher energy density, but the diffusion control step of ions in electrode materials leads to lower power density. At the same time, the embedding and de-embedding of ions will change the material structure and greatly reduce the cycle life of the electrode. SCS is the adsorption of ions in the electrolyte on the surface of the electrode material. Based on the principle of ion physical adsorption at the electrode / electrolyte interface, the ion adsorption and desorption rate is fast, so it can provide higher power density, and the electrode material structure does not change, so it has a longer cycle life. However, since SCS charge storage only uses the surface of the electrode material, the energy density obtained is limited.

[0003] Carbon materials have become one of the earliest electrode materials used in supercapacitors due to their advantages such as low price, high specific surface area, good conductivity and excellent chemical stability. Currently, commercial supercapacitors use activated carbon as electrode material, but its specific capacitance is relatively low. Manganese dioxide (MnO2) has the advantages of abundant resources, low cost and non-toxicity, multiple oxidation states and high theoretical specific capacity, making it an ideal pseudocapacitive electrode material for supercapacitors. A large number of studies have found that the main factors affecting the electrochemical performance of manganese dioxide electrodes include crystal form, conductivity and specific surface area, and the use of a single material itself expands in volume during the cycle and has poor conductivity. When carbon materials are introduced into MnO2 materials to form composite materials, their conductivity can be effectively improved to obtain composite electrode materials with significant electrochemical properties.

[0004] Although there are many methods for synthesizing hollow carbon sphere / manganese dioxide composites, most of them remain in the relatively ideal environment and working conditions in the laboratory. When put into industrial production, there are many variable factors, and the process in the experimental scenario is difficult to reproduce in the factory. The resulting composite materials have poor stability and irregular and uneven appearance, so the existing technology is not conducive to industrial production. Summary of the invention

[0005] The present invention aims to provide a method for preparing a hollow carbon sphere-coated manganese dioxide composite material to solve a series of problems such as poor material stability and uneven appearance when the prior art is applied to industrial production of hollow carbon sphere / manganese dioxide composite materials.

[0006] A method for preparing a hollow carbon sphere-coated manganese dioxide composite material in this scheme comprises the following steps:

[0007] 1) Preparation of SiO2@PDA silicon spheres: ammonia water, ethanol, pure water and tetraethyl orthosilicate were mixed and stirred, and dopamine hydrochloride was added, and the SiO2@PDA silicon spheres were obtained after reaction and drying;

[0008] 2) Preparation of hollow carbon spheres: The obtained SiO2@PDA silicon spheres were sintered under high temperature nitrogen protection conditions and soaked in hydrofluoric acid to obtain hollow carbon spheres;

[0009] 3) Preparation of hollow carbon sphere-coated manganese dioxide composite material: The obtained hollow carbon sphere is added into KMnO4 aqueous solution to react to obtain the hollow carbon sphere-coated manganese dioxide composite material.

[0010] Furthermore, in step 1), after mixing ammonia water, ethanol, pure water and tetraethyl orthosilicate, the solution after dopamine hydrochloride reaction is added and centrifuged, and then washed with deionized water for several times and dried at 75-90° C. to obtain SiO2@PDA silicon spheres.

[0011] Furthermore, in step 1), the volume ratio of tetraethyl orthosilicate to dopamine hydrochloride is 1:15-25.

[0012] Furthermore, in step 1), the mixing and stirring reaction time after adding dopamine hydrochloride is ≥ 24 hours.

[0013] Further, in step 2), the obtained SiO2@PDA silicon spheres are sintered at 800-900°C under nitrogen protection for 2 hours with a heating rate of 5°C / min.

[0014] Furthermore, in step 2), analytically pure hydrofluoric acid with a concentration of 5% is used for immersion for more than 24 hours.

[0015] Furthermore, the concentration of the KMnO4 solution in step 3) is 20 mmol / l.

[0016] Furthermore, the reaction temperature in step 3) is 130-150° C., and the reaction time is 2 h.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) The present invention designs the growth of MnO2 particles on the surface of hollow porous carbon nanospheres to prepare a new type of spherical composite material with a hollow structure, which is beneficial to ion diffusion and increases the reactive surface area of ​​the electrode material and has good capacitance characteristics at different rates.

[0019] 2) The composite material designed by the present invention is named hollow carbon sphere-coated manganese dioxide composite material. Because transition metal oxides that can participate in redox reactions are grown on hollow carbon spheres, the capacity of existing carbon materials is greatly improved, and the structure and electrochemical properties of supercapacitor carbon materials are improved.

[0020] 3) This method can be applied to industrial production to prepare hollow carbon sphere-coated manganese dioxide composite materials with uniform and stable shapes, which is conducive to mass production and promotes the improvement of the cyclic stability of the composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The scanning electron microscope image (a) and the transmission electron microscope image (b) of the hollow carbon sphere-coated manganese dioxide composite material prepared in Example 1 of the present invention.

[0022] Figure 2 The X-ray diffraction patterns of dopamine-coated silica spheres (C-1), hollow carbon spheres (C-2), and hollow carbon sphere-coated manganese dioxide composite materials (C-3) in Example 1 of the present invention.

[0023] Figure 3 The charge and discharge curves of the hollow carbon sphere-coated manganese dioxide composite material prepared in Example 1 of the present invention at different current densities.

[0024] Figure 4 The hollow carbon sphere-coated manganese dioxide composite material prepared in Example 1 of the present invention is subjected to 10A﹒ g- 1 Charge and discharge cycle curves under . DETAILED DESCRIPTION

[0025] Embodiment 1: A method for preparing a hollow carbon sphere-coated manganese dioxide composite material, comprising the following steps:

[0026] 1) Preparation of SiO2@PDA silicon spheres: First, 1 ml of ammonia water, 20 ml of ethanol, 80 ml of water and 1 ml of tetraethyl orthosilicate were measured, mixed and stirred for 30 min, and then 20 mg of dopamine hydrochloride was added, and the mixture was mixed and stirred for 24 h. After the reaction, the solution was centrifuged at 8000 rpm for 5 min, and then washed with deionized water for 5 times and dried at 80°C for 12 h to obtain SiO2@PDA silicon spheres;

[0027] 2) Preparation of hollow carbon spheres: The obtained SiO2@PDA silicon spheres were sintered at 800°C under N2 protection for 2 h (heating rate 5°C / min), and then soaked in 5% HF for 24 h. After the reaction, the solution was centrifuged at 8000 rpm for 5 min, washed with deionized water 5 times, and dried at 80°C for 12 h to obtain hollow carbon spheres.

[0028] 3) Preparation of hollow carbon sphere-coated manganese dioxide composite materials: The obtained hollow carbon spheres were added to an aqueous solution consisting of 50 ml of water and 20 mmol / l KMnO4, heated to 140°C, and stirred for reaction for 2 hours. After the reaction, the solution was centrifuged at 8000 rpm for 5 minutes, washed with deionized water 5 times, and dried at 80°C for 12 hours to obtain a hollow carbon sphere-coated manganese dioxide composite material.

[0029] The preparation process of this method is relatively simple and can be mass-produced. Figure 1 (a) is a scanning electron microscope image of the composite material, showing that the MnO2-coated carbon spheres are hollow structures. Figure 1 (b) is a transmission electron microscopy image of the composite material, from which it can be seen that the spherical structure is complete and MnO2 grows evenly.

[0030] Figure 2 is the X-ray diffraction diagram of the composite material. The characteristic peaks of the carbon spheres are all in the range of 20° to 30°. After C-1 is doped with N, the interplanar spacing of the coating material increases, causing the characteristic peak to shift to a larger angle. C-2 is a hollow structured carbon sphere formed after HF etching. C-3 is a hollow carbon sphere formed after manganese doping. The characteristic peak shifts to a larger angle, indicating that the interlayer spacing of the composite material is greater than that of the other two materials, which is more conducive to ion transmission and has better large current discharge capability.

[0031] Figure 3 The charge and discharge curves of the composite material at different current densities are shown in Table 1. According to the charge and discharge cycle conditions, the discharge specific capacitance can be obtained by the specific capacitance calculation formula.

[0032] Table 1 Discharge specific capacitance of the obtained composite materials at different current densities

[0033] Current density <![CDATA[1A﹒g -1 ]]> <![CDATA[2A﹒g -1 ]]> <![CDATA[4A﹒g -1 ]]> <![CDATA[5A﹒g -1 ]]> <![CDATA[10A﹒g -1 ]]> <![CDATA[20A﹒g -1 ]]> Discharge specific capacitance <![CDATA[198F﹒g -1 ]]> <![CDATA[188F﹒g -1 ]]> <![CDATA[192F﹒g -1 ]]> <![CDATA[183F﹒g -1 ]]> <![CDATA[176F﹒g -1 ]]> <![CDATA[168F﹒g -1 ]]>

[0034] Embodiment 2: A preparation method and application of a hollow carbon sphere-coated manganese dioxide composite material, comprising the following steps:

[0035] 1) Preparation of SiO2@PDA silicon spheres: First, 2 ml of ammonia water, 40 ml of ethanol, 150 ml of water and 2 ml of tetraethyl orthosilicate were measured, mixed and stirred for 30 min, and then 40 mg of dopamine hydrochloride was added, and the mixture was mixed and stirred for 24 h. After the reaction, the solution was centrifuged at 8000 rpm for 5 min, and then washed with deionized water for 5 times and dried at 80°C for 12 h to obtain SiO2@PDA silicon spheres;

[0036] 2) Preparation of hollow carbon spheres: The obtained SiO2@PDA silicon spheres were sintered at 800°C under N2 protection for 2 h (heating rate 5°C / min), and then soaked in 5% HF for 24 h. After the reaction, the solution was centrifuged at 8000 rpm for 5 min, washed with deionized water 5 times, and dried at 80°C for 12 h to obtain hollow carbon spheres.

[0037] 3) The obtained hollow carbon spheres were added to an aqueous solution consisting of 100 ml of water and 40 mmol / l KMnO4, heated to 140°C, and stirred for reaction for 2 hours. After the reaction, the solution was centrifuged at 8000 rpm for 5 minutes, washed with deionized water 5 times, and dried at 80°C for 12 hours to obtain a hollow carbon sphere-coated manganese dioxide composite material.

[0038] Electrochemical performance test:

[0039] A three-electrode system was assembled using a hollow carbon ball-coated manganese dioxide composite material as the positive electrode (the mass of the coated composite material was 1 mg), a platinum sheet electrode as the negative electrode, and a SHE electrode as the reference electrode. A 1M Na2SO4 solution was used as the electrolyte to test the electrochemical performance in the voltage range of 0.8V to 1.8V (vs. SHE). (a) Figure 3 , at 1A﹒ g -1 ,2A﹒ g -1 ,4A﹒ g -1 , 5A﹒ g -1 , 10A﹒ g -1 , 20A﹒ g -1 The charge and discharge cycles showed that the discharge specific capacitance was 198F﹒ g -1 , 188F﹒ g -1 , 192F﹒ g -1 , 183F﹒ g -1 , 176F﹒ g -1 , 168F﹒ g -1 (b) if Figure 4 , at 10A﹒ g -1 The initial reversible specific capacitance is 179F﹒ g -1 After the cyclic charge and discharge begins, the specific capacitance increases slowly and stabilizes at 198 F﹒ g after 2000 cycles. -1 After 5000 cycles, the specific capacitance remains at 197F﹒g -1 above.

Claims

1. A method for preparing a hollow carbon sphere-coated manganese dioxide composite material, characterized in that The following steps are involved: 1) Preparation of SiO2@PDA silicon spheres: ammonia water, ethanol, pure water and tetraethyl orthosilicate were mixed and stirred, and dopamine hydrochloride was added, and the SiO2@PDA silicon spheres were obtained after reaction and drying; 2) Preparation of hollow carbon spheres: The obtained SiO2@PDA silicon spheres were sintered under high temperature nitrogen protection conditions and soaked in hydrofluoric acid to obtain hollow carbon spheres; 3) Preparation of hollow carbon sphere-coated manganese dioxide composite material: The obtained hollow carbon sphere is added into KMnO4 aqueous solution to react to obtain the hollow carbon sphere-coated manganese dioxide composite material.

2. The method for preparing a hollow carbon sphere-coated manganese dioxide composite material according to claim 1, characterized in that: In step 1), ammonia water, ethanol, pure water and tetraethyl orthosilicate are mixed and stirred, dopamine hydrochloride is added to the reacted solution, and the solution is centrifuged and then washed with deionized water for several times and dried at 75-90° C. to obtain SiO2@PDA silicon spheres.

3. The method for preparing a hollow carbon sphere-coated manganese dioxide composite material according to claim 2, characterized in that: In step 1), the volume ratio of tetraethyl orthosilicate to dopamine hydrochloride is 1:15-25.

4. The method for preparing a hollow carbon sphere-coated manganese dioxide composite material according to claim 3, characterized in that: After adding dopamine hydrochloride in step 1), the mixing and stirring reaction time is ≥ 24 hours.

5. The method for preparing a hollow carbon sphere-coated manganese dioxide composite material according to claim 4, characterized in that: In step 2), the obtained SiO2@PDA silicon spheres are sintered at 800-900°C under nitrogen protection for 2 hours with a heating rate of 5°C / min.

6. The method for preparing a hollow carbon sphere-coated manganese dioxide composite material according to claim 5, characterized in that: In step 2), analytically pure hydrofluoric acid with a concentration of 5% is used for soaking for more than 24 hours.

7. The method for preparing a hollow carbon sphere-coated manganese dioxide composite material according to claim 6, characterized in that: The concentration of the KMnO4 solution in step 3) is 20 mmol / l.

8. The method for preparing a hollow carbon sphere-coated manganese dioxide composite material according to claim 7, characterized in that: The reaction temperature in step 3) is 130-150° C. and the reaction time is 2 h.

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