阅读说明：本技术 一种用于锂硫电池正极材料的3D-ZIF8@zif67制备方法 (Preparation method of 3D-ZIF8@ ZIF67 for lithium-sulfur battery cathode material ) 是由 王新 张俊凡 于 2019-09-16 设计创作，主要内容包括：本发明涉及一种锂硫电池正极材料的制备方法,所述锂硫电池正极材料为具有三维有序介孔的ZIF67和ZIF8的复合材料,记为3D-ZIF67@ZIF8。本发明所述方法首先制备PS球,随后将PS球与六水合硝酸钴和六水合硝酸锌溶液以及2-甲基咪唑的甲醇溶液混合反应制备PS-ZIF67@ZIF8材料,最终通过碳化得到3D-ZIF67@ZIF8材料。本发明的制备方法简单、可控,其丰富的多孔结构,以及碳化后高的C含量,不但可以改善硫的导电性,而且能够阻止放电产物多硫化物的溶解并缓解体积膨胀。(The invention relates to a preparation method of a lithium-sulfur battery anode material, wherein the lithium-sulfur battery anode material is a composite material of ZIF67 and ZIF8 with three-dimensional ordered mesopores, and is marked as 3D-ZIF67@ ZIF 8. The method comprises the steps of firstly preparing a PS ball, then mixing and reacting the PS ball with cobalt nitrate hexahydrate, zinc nitrate hexahydrate solution and methanol solution of 2-methylimidazole to prepare a PS-ZIF67@ ZIF8 material, and finally carbonizing to obtain a 3D-ZIF67@ ZIF8 material. The preparation method is simple and controllable, has rich porous structure and high C content after carbonization, can improve the conductivity of sulfur, and can prevent polysulfide of a discharge product from dissolving and relieve volume expansion.)

1. A preparation method of a lithium-sulfur battery positive electrode material is a composite material 3D-ZIF67@ ZIF8 of ZIF67 and ZIF8 with 3D ordered mesopores, and comprises the following steps:

the first step is as follows: preparation of PS spheres

Adding 10-20 parts by mass of styrene and 10-20 parts by mass of polyvinylpyrrolidone into 50-100 parts by mass of deionized water, stirring for 2-5h, then stirring oil bath in a round-bottom flask at 70-80 ℃, stirring for 12-24h, performing centrifugal separation, and drying at 60-80 ℃ to obtain PS balls;

the second step is that: preparing PS ball/ZIF 67/ZIF8 material

Dispersing 5-10mmol of cobalt nitrate hexahydrate and zinc nitrate hexahydrate in 250ml of methanol, and recording as solution A, wherein the molar ratio of the cobalt nitrate hexahydrate to the zinc nitrate hexahydrate is 1: 1; dispersing 20-40mmol of 2-methylimidazole in 250ml of methanol, and marking as liquid B; adding the solution B into the solution A with the same volume, stirring uniformly, adding 1-2g of the PS balls prepared in the first step, sealing, standing and aging for a certain time, centrifuging, washing, and drying at 60-80 ℃ overnight to obtain PS-ZIF67@ ZIF 8;

the third step: carbonizing

And (3) placing the PS-ZIF67@ ZIF8 prepared in the second step in a tubular furnace, heating to 600-fold air temperature of 700 ℃ in Ar atmosphere, preserving the heat for 1-2 hours, and then naturally cooling to obtain 3D-ZIF67@ ZIF 8.

2. The preparation method according to claim 1, wherein in the step, the stirring is magnetic stirring, and the stirring speed is 100-300 r/min.

3. The method of claim 1 or 2, wherein the centrifugation is performed at 800rad/min in the first step and the centrifugation is repeated 3 times.

4. The method according to claim 1 or 2, wherein in the second step, the aging time is 24 hours.

5. The production method according to claim 1 or 2, wherein in the second step, the centrifugal washing is 3 times of washing with methanol and 3 times of washing with ethanol in this order.

6. The production method according to claim 1 or 2, wherein in the third step, the temperature increase rate is 1 to 2 ℃/min.

Technical Field

The invention relates to a preparation method of a 3D ordered ZIF67/ZIF 8/sulfur composite material used as a lithium-sulfur battery anode material, belonging to the field of material chemistry.

Background

With the rapid development of society, the demand of human beings on energy sources is increasing. However, as the living standard of people is continuously improved, some main fossil energy sources, such as coal, oil and natural gas, are in increasing shortage. At the same time, the combustion of some fossil energy, with the resulting environmental pollution and destruction, is irreparable. For example, the greenhouse effect is caused by excessive emission of carbon dioxide, and the continuous emission of automobile exhaust gas also causes the gradual rise of the sea level, and the gradual deterioration of the haze is caused, so that the health and living environment of human beings are seriously threatened. Therefore, research on new renewable clean energy and energy storage devices is urgent. Although the novel energy sources such as wind energy, solar energy and tidal energy are clean and pollution-free, the novel energy sources are limited by energy sources and cannot replace internal combustion engines to provide stable energy sources for vehicles and the like. The battery as a novel, high-energy and pollution-free chemical power source has been widely applied to the field of energy storage of portable electronic equipment, electric automobiles and the like, and has entered the field of vision of people and gained wide attention and research as an energy storage device with high specific capacity and long cycle life. At present, the theoretical specific capacity of the commercialized lithium ion battery anode material is limited by the theoretical specific capacity of 300mAh/g, and cannot meet the requirement on the practical application quality of the lithium ion battery, and the theoretical specific capacity of the novel lithium sulfur battery is about five times of the theoretical specific capacity of the existing commercial lithium ion battery anode material (the theoretical specific capacity is 1675mAh/g, and the specific energy is 2500Wh/kg), and is considered to be one of the high-energy batteries with the most development potential.

However, lithium sulfur batteries have many obstacles in practical use. First, pure sulfur is an insulator at room temperature, and the transport of electrons and ions in a positive electrode using sulfur as a positive electrode material is very difficult. Secondly, the intermediate product lithium polysulfide formed in the charging and discharging process is easily dissolved in the electrolyte solution, so that the electroactive substances on the positive electrode are pulverized, dropped and dissolved to lose, the lithium polysulfide dissolved in the electrolyte is diffused to the lithium metal negative electrode, and the lithium sulfide generated by the reaction is precipitated on the surface of the negative electrode, so that the internal resistance of the battery is increased, and finally the capacity of the battery is attenuated. Third, sulfur and final product Li₂The sulfur positive electrode undergoes volume expansion and fragmentation (expansion ratio of 76%) depending on the density of S, which results in poor cycle stability of the lithium-sulfur battery.

The metal organic frame material, MOFs for short, forms a junction due to the controllable and changeable structureThe structure has more pores and larger specific surface area, thereby having excellent capability of reacting with small molecules. In recent years, MOFs have not only demonstrated their superiority and diversity in gas storage and separation, sensing, catalysis, and drug delivery, but also started to be studied intensively in the field of electrochemistry and gradually emerged. Nowadays, the preparation of electrode materials from MOFs as precursors is common. However, there are not many reports that MOFs are directly applied as a material for a negative electrode of a lithium ion battery. The MOFs has larger specific surface area, effectively increases the contact area with an electrolyte, and simultaneously, the controllable porous structure also enables Li⁺The electrode material is easier to be embedded and separated, and the electrochemical performance is improved. The research on MOFs is beneficial to the better development of lithium ion batteries, so that the development of a metal organic framework material with higher reversible capacity and better cycle stability is of great significance.

Among the numerous metal organic frameworks, ZIF8 (Zn-based) and ZIF67 (Co-based) have novel structures, and Zn and Co-based organic frameworks can provide a large specific surface area, have abundant micropores, facilitate adsorption of lithium polysulfide, and can be loaded with more S.

Disclosure of Invention

The invention aims to provide a preparation method of a 3D ordered mesoporous ZIF67 and ZIF8 composite material, which is used as a positive electrode of a lithium-sulfur secondary battery, has the characteristics of high capacity and stable cycle performance, and can prolong the cycle life of a sulfur electrode material. In order to achieve the purpose, the technical scheme of the invention is as follows:

a preparation method of a lithium-sulfur battery positive electrode material is characterized in that the lithium-sulfur battery positive electrode material is a composite material of ZIF67 and ZIF8 with 3D ordered mesopores, and is marked as 3D-ZIF67@ ZIF8, and the preparation method comprises the following preparation steps: the first step is as follows: preparation of PS spheres

Adding 10-20 parts by mass of styrene and 10-20 parts by mass of polyvinylpyrrolidone into 50-100 parts by mass of deionized water, stirring for 2-5h, then stirring an oil bath in a round bottom flask, wherein the temperature of the oil bath is 70-80 ℃, and stirring for 12-24 h. Then centrifuging for 3 times at the rotating speed of 800rad/min, and drying at the temperature of 60-80 ℃ to obtain the PS balls. The second step is that: preparing PS ball/ZIF 67/ZIF8 material

Dispersing 5-10mmol of cobalt nitrate hexahydrate and zinc nitrate hexahydrate in 250ml of methanol, and recording as solution A, wherein the molar ratio of the cobalt nitrate hexahydrate to the zinc nitrate hexahydrate is 1: 1; dispersing 20-40mmol of 2-methylimidazole in 250ml of methanol, and marking as liquid B; and adding the solution B into the solution A with the same volume, adding 1-2g of the PS balls prepared in the first step, stirring for 3-5min to be uniform, sealing, standing and aging for a certain time, centrifugally washing, washing for 3 times by using methanol, washing for 3 times by using ethanol, and drying at 60-80 ℃ overnight to obtain the PS-ZIF67@ ZIF 8.

The third step: carbonizing

And (3) placing the PS-ZIF67@ ZIF8 in the second step under a tubular furnace, heating to 600-fold sand 700 ℃ in Ar atmosphere, preserving the heat for 1-2h at the heating speed of 1-2 ℃/min, and then naturally cooling to obtain the 3D-ZIF67@ ZIF 8.

The stirring in the steps is magnetic stirring, and the rotating speed is 100-300 r/min.

The preparation method of the lithium-sulfur battery positive electrode material has the following beneficial effects:

the ordered 3D-ZIF67@ ZIF8 composite carbon nanotube material is prepared by using a simple test method and process steps, holes in the material can well adsorb polysulfide, the utilization rate of sulfur is improved, the carbonized material has good conductivity, and ZnO and Co have good conductivity₃O₄The synergistic effect is to adsorb polysulfides even more.

The above-mentioned method for preparing the lithium-sulfur battery separator material involves raw materials that are commercially available, and the equipment and processes used are well known to those skilled in the art.

Drawings

The invention is further illustrated with reference to the following figures and examples.

FIG. 1 is a graph showing the cycle performance of the 3D-ZIF67@ ZIF8/S composite material prepared in example 1.

FIG. 2 is a charge-discharge curve of the 3D-ZIF67@ ZIF8/S composite material prepared in example 2 at 1C.

FIG. 3 is a scanned picture of 3D-ZIF67@ ZIF8 prepared in example 2.

Detailed Description