阅读说明：本技术 二氧化锰纳米粒子修饰的三维分级多孔碳网络及其制备方法与应用 (Manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network and preparation method and application thereof ) 是由 闵宇霖 丁香玉 时鹏辉 范金辰 徐群杰 于 2019-09-11 设计创作，主要内容包括：本发明以一种天然水凝胶-琼脂为原料,利用琼脂溶于沸水,冷却后琼脂分子内部和分子间形成氢键而成的凝胶,再通过冷冻干燥技术除去水分,然后将其高温碳化形成碳材料,在形凝胶过程中将金属离子成功引入碳基底中,高温碳化后成功制备了二氧化锰纳米粒子修饰的三维多孔碳网络复合材料。将合成的材料应用于锂硫电池正极宿主材料时,其载硫量高达76.3％,分级多孔(大孔,介孔,微孔)网络结构对多硫化物有着很好的限制作用,且多孔的网络结构有利于电解液的浸润,另外,二氧化锰纳米粒子对多硫化物也有着很好的吸附作用,有效抑制了锂硫电池的穿梭效应。本发明选用材料价格低廉,简单易得,在未来的能量储存方面有较好的应用前景。(The invention takes a natural hydrogel-agar as a raw material, the agar is dissolved in boiling water, the agar forms a gel formed by hydrogen bonds in and among agar molecules after being cooled, moisture is removed by a freeze-drying technology, then the agar molecules are carbonized at high temperature to form a carbon material, metal ions are successfully introduced into a carbon substrate in the process of forming the gel, and the manganese dioxide nano particle modified three-dimensional porous carbon network composite material is successfully prepared after high-temperature carbonization. When the synthesized material is applied to a lithium-sulfur battery anode host material, the sulfur carrying amount of the synthesized material is up to 76.3%, the hierarchical porous (macroporous, mesoporous, microporous) network structure has a good limiting effect on polysulfide, the porous network structure is favorable for the infiltration of electrolyte, in addition, manganese dioxide nanoparticles have a good adsorption effect on polysulfide, and the shuttle effect of the lithium-sulfur battery is effectively inhibited. The material selected by the invention has low price, is simple and easy to obtain, and has better application prospect in the aspect of future energy storage.)

1. A preparation method of a manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network is characterized by comprising the following steps:

step 1: preparing a manganese acetate aqueous solution, adding agar powder, magnetically stirring for 30-60 min, raising the temperature to 100 ℃, continuously magnetically stirring until agar is completely dissolved, and heating at 100 ℃ for 1-3 h to obtain a colloidal solution;

step 2: ultrasonically defoaming the colloidal solution obtained in the step 1, naturally cooling to room temperature to form hydrogel, quickly freezing by using liquid nitrogen, and freeze-drying in a freeze dryer for 3 d;

and step 3: shearing the aerogel obtained after freeze-drying and dehydration in the step 2, placing the sheared aerogel in a tube furnace, and calcining the sheared aerogel at high temperature in an argon atmosphere;

and 4, step 4: and (3) mixing the sample obtained by high-temperature calcination in the step (3) with solid KOH according to the mass ratio of 1:3, grinding into powder, placing the powder in a tube furnace, activating at the high temperature of 500-700 ℃ for 1-2 h under the nitrogen atmosphere, washing, centrifugally collecting, placing the powder in a vacuum drying box, vacuum drying at the temperature of 60-80 ℃ for 8-12 h, and grinding to obtain the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network.

2. The preparation method of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network according to claim 1, wherein the concentration of manganese acetate in the manganese acetate aqueous solution in the step 1 is 5-10mg/mL, and the mass-to-volume ratio of the agar powder to the manganese acetate aqueous solution is 0.01-0.05 g/mL.

3. The preparation method of the manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network according to claim 1, wherein in the step 3, the specific conditions of high-temperature calcination are as follows: keeping the temperature at 100 ℃ for 2h, keeping the temperature at 300 ℃ for 5h, keeping the temperature at 400 ℃ for 12h, keeping the temperature at 700 ℃ for 5h, and keeping the temperature rise rate at 1-5 ℃/min.

4. The method for preparing the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network according to claim 1, wherein the washing in the step 4 is performed by washing with 0.1mol/L diluted HCl and deionized water for several times respectively, and finally washing with water until the network is neutral.

5. The manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network prepared by the method of any one of claims 1 to 4, characterized in that the microstructure thereof is a manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network structure with macropores, mesopores and micropores existing simultaneously.

6. The manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network of claim 5, wherein the doping amount of C atoms in the manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network is 85-95 wt%.

7. The manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network of claim 5, wherein the doping amount of O atoms in the manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network is 2.5-5 wt%.

8. The manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network of claim 5, wherein the doping amount of Mn atoms in the manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network is 2.5-5 wt%.

9. The application of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network prepared by the method of any one of claims 1 to 4 in preparation of a lithium-sulfur battery positive host material.

Technical Field

The invention belongs to the field of materials science, relates to a lithium-sulfur battery positive electrode material, and particularly relates to a three-dimensional hierarchical porous carbon network modified by transition metal oxide manganese dioxide nanoparticles and a preparation method thereof.

Background

Lithium Sulfur Batteries (LSBs) have a capacity of up to 1675mA h g^-1Theoretical specific capacity of, and 2600W h kg^-1Has become one of the most promising second generation energy storage devices. In addition, sulfur is abundant in the earth, low in cost and low in toxicity, and thus has attracted extensive attention of researchers. However, the lithium-sulfur battery still has many problems that limit its practical application, such as: (1) the conductivity of both sulfur and lithium sulfide was poor (25 ℃ C.,. apprxeq.5X 10-30S m)^-1) When used directly as a positive electrode material, the battery reaction hardly proceeds; (2) during charge and discharge cycles, the volume of the electrode material will expand severely (-80%), leading to electrode material pulverization, resulting in poor contact between the active material and the current collector, further hindering reaction kinetics; (3) intermediate polysulfide (Li)₂S_nN is more than or equal to 4 and less than or equal to 8) is easy to dissolve in electrolyte, so that shuttle effect is caused, and the coulomb efficiency of the battery is reduced; (4) the sulfur host material has a lower sulfur loading.

Researchers solve the problems encountered by the lithium-sulfur battery from different aspects, wherein a porous carbon material attracts people's attention, and a carbon-sulfur composite material is prepared to be used as a conductive framework of a positive electrode material and used for enhancing and improving the defect of poor sulfur conductivity; secondly, the porous carbon skeleton acts as a physical barrier to limit the "shuttling effect" of lithium polysulfides; due to the high conductivity, various redox reactions of the sulfur anode can be carried out, and redox intermediates can be efficiently captured; the porous structure has higher specific surface area, and can improve the loading of sulfur. Therefore, the rational design of the porous network carbon material with hierarchical porosity and internal crosslinking is always a research hotspot of the scientific community, wherein the pore size plays a crucial role in improving the electrochemical performance of the lithium-sulfur battery. The following are advantages and disadvantages of carbon materials of different pore sizes in lithium sulfur battery applications: the microporous carbon material (the aperture is less than 2nm) can effectively limit the shuttling of soluble lithium polysulfide and reduce the shuttling effect, but the aperture is too small, the aperture is easily blocked by a solid product and is not beneficial to the electrolyte permeation in the discharging process, and in addition, the loading capacity of sulfur is lower due to the too small aperture; macroporous carbon materials (pore size >50nm) can hold a large amount of sulfur, but the pores are too large to easily cause dissolution of lithium polysulfide; mesoporous carbon materials (2nm and less than or equal to 50nm) are considered as the most ideal strategy; however, the single use of mesoporous materials still cannot effectively inhibit the dissolution of lithium polysulfide and promote the permeation of electrolyte in electrode materials, so there is an urgent need to combine the advantages of materials with different pore diameters to synthesize porous materials with multiple scales to overcome the inherent limitations of porous materials with single scale. In recent years, many hierarchical porous carbon materials containing both macropores, micropores and mesopores have been used in lithium sulfur batteries, but still have some drawbacks such as rapid capacity fade due to a polarity difference between the carbon material and lithium polysulfide, shuttle effect of polysulfide not being effectively limited, and structural integrity of the positive electrode material during charge and discharge cannot be maintained.

Disclosure of Invention

The invention aims to provide a manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network and a preparation method thereof.

In order to achieve the aim, the invention provides a preparation method of a manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network, which is characterized by comprising the following steps of:

step 1: preparing a manganese acetate aqueous solution, adding agar powder, magnetically stirring for 30-60 min, raising the temperature to 100 ℃, continuously magnetically stirring until agar is completely dissolved, and heating at 100 ℃ for 1-3 h to obtain a colloidal solution;

step 2: ultrasonically defoaming the colloidal solution obtained in the step 1, naturally cooling to room temperature to form hydrogel, quickly freezing by using liquid nitrogen, and freeze-drying in a freeze dryer for 3 d;

and step 3: shearing the aerogel obtained after freeze-drying and dehydration in the step 2, placing the sheared aerogel in a tube furnace, and calcining the sheared aerogel at high temperature in an argon atmosphere;

and 4, step 4: and (3) mixing the sample obtained by high-temperature calcination in the step (3) with solid KOH according to the mass ratio of 1:3, grinding into powder, placing the powder in a tube furnace, activating at the high temperature of 500-700 ℃ for 1-2 h under the nitrogen atmosphere, washing, centrifugally collecting, placing the powder in a vacuum drying box, vacuum drying at the temperature of 60-80 ℃ for 8-12 h, and grinding to obtain the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network.

Preferably, the concentration of manganese acetate in the manganese acetate aqueous solution in the step 1 is 5-10mg/mL, and the mass-to-volume ratio of the agar powder to the manganese acetate aqueous solution is 0.01-0.05 g/mL.

Preferably, in the step 3, the specific conditions of the high-temperature calcination are as follows: keeping the temperature at 100 ℃ for 2h, keeping the temperature at 300 ℃ for 5h, keeping the temperature at 400 ℃ for 12h, keeping the temperature at 700 ℃ for 5h, and keeping the temperature rise rate at 1-5 ℃/min.

Preferably, the washing in the step 4 is washing with 0.1mol/L diluted HCl and deionized water respectively for several times, and finally washing with water to be neutral.

The invention also provides the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network prepared by the method, which is characterized in that the microstructure of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network is a three-dimensional hierarchical porous carbon network structure with macropores, mesopores and micropores existing simultaneously.

Preferably, in the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network, the doping amount of C atoms is 85-95 wt%,

preferably, in the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network, the doping amount of O atoms is 2.5-5 wt%,

preferably, in the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network, the doping amount of Mn atoms is 2.5-5 wt%.

The invention also provides application of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network prepared by the method in preparation of a lithium-sulfur battery anode host material.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention uses a natural hydrogel-agar as a raw material, the agar is dissolved in boiling water, the agar forms a gel by hydrogen bonds in and among molecules after being cooled, moisture is removed by a freeze-drying technology, then the agar is carbonized at high temperature to form a carbon material, metal ions are successfully introduced into a carbon substrate in the process of gel forming, and the three-dimensional porous carbon network composite material modified by metal oxide nano particles is successfully prepared after high-temperature carbonization. The synthetic method is simple and easy to implement, and has small harm to the environment, when the synthetic material is applied to the lithium-sulfur battery anode host material, the sulfur carrying amount is up to 76.3%, in addition, the hierarchical porous (macroporous, mesoporous, microporous) network structure has good limiting effect on polysulfide, the porous network structure is favorable for the infiltration of electrolyte, in addition, manganese dioxide nano particles also have good adsorption effect on polysulfide, and the shuttle effect of the lithium-sulfur battery is effectively inhibited.

(2) The invention has cheap and easily obtained raw materials, simple preparation method and no addition of any hard template, synthesizes the three-dimensional carbon-based composite material which is modified by the inorganic transition metal oxide nano particles and has hierarchical porosity, is suitable for large-scale production, reduces the cost, contributes to arousing the attention of people to energy crisis and has better prospect in the future energy storage direction.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) picture of a manganese dioxide nanoparticle-modified three-dimensional hierarchical porous carbon network of example 1;

FIG. 2a is a nitrogen sorption and desorption curve of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 1;

FIG. 2b is a plot of the pore size distribution of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 1;

FIG. 3a is a Raman (Raman) plot of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 1;

FIG. 3b is a thermogravimetric analysis (TGA) plot of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 1;

FIG. 3c is an X-ray diffraction (XRD) pattern of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 1;

FIG. 3d is a graph of infrared spectroscopic analysis (FT-IR) of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 1;

FIG. 4 is an X-ray photoelectron spectroscopy (XPS) plot of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 1;

FIG. 5 is a graph of the alternating current impedance (EIS) and Cyclic Voltammogram (CV) at a sweep rate of 0.1mV s-1 for the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 4;

FIG. 6 is a graph of electrochemical performance of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of example 4, (a) cycling performance of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network (HPCM/S) and HPC/S without manganese dioxide nanoparticle modification; (b) constant current charge and discharge curve of HPCM/S; (c) charging and discharging curves of HPCM/S and HPC/S at a current density of 0.2C; (d) multiplying power performance diagrams (e) of HPCM/S and HPC/S the charging and discharging curves of HPCM/S at current densities of 0.1C,0.2C,0.5C,1C,2C, respectively;

FIG. 7 is a schematic flow chart of the preparation process of the manganese dioxide nanoparticle modified three-dimensional hierarchical porous carbon network of the present invention.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.