High-performance lithium-sulfur battery positive electrode material and preparation method thereof

Abstract

The invention relates to a high-performance lithium-sulfur battery positive electrode material and a preparation method thereof. The preparation method of the high-performance lithium-sulfur battery positive electrode material comprises the following steps of S1, preparing graphene oxide by employing an improved Hummers method; and S2, dropwise adding a nanometer sulfur solution into a graphene oxide solution under a stirring condition to obtain a mixed liquid, performing ultrasonic dispersion on the mixed liquid for 1-5 hours under a power of 300-650W, and finally, performing spray drying onthe mixed liquid to obtain the high-performance lithium-sulfur battery positive electrode material, wherein the pressure of spray drying is standard atmospheric pressure, the air inlet quantity is (2-8)m<3> per minute, the air inlet temperature is 150-250 DEG C, the feeding speed is (1-10)mL per minute, and the pin through speed is one time per 5-30 seconds. The lithium-sulfur battery positive electrode prepared by the method has relatively high loading quantity and is excellent in electrochemical property and high in stability, and a shuttling effect and a volume expansion effect can be effectively prevented.

Description

technical field [0001] The invention relates to the field of material technology, in particular to a high-performance lithium-sulfur battery cathode material and a preparation method thereof. Background technique [0002] With the ever-expanding fields of batteries such as hybrid vehicles, smart grids, portable products, etc., higher and higher requirements are placed on their performance. At present, traditional commercial lithium-ion batteries are limited by their own theoretical specific capacity of 300mAh / g, resulting in low energy density, and it is difficult to meet the quality requirements of lithium-ion batteries for practical applications. Therefore, it is of great strategic significance to develop next-generation lithium-ion secondary batteries with high energy density, environmental protection and low cost. The theoretical specific capacity of the new lithium-sulfur battery is 2600Wh / kg, about five times that of the traditional commercial lithium-ion battery, and...

AI Technical Summary

Problems solved by technology

[0005] The fundamental defect in the existing technology CN201710242972.5 in the process of preparing lithium-sulfur battery cathode materials is: (a) the patented technology uses hydrothermal method to do in-situ sulfur, and graphene and sulfur are compounded during the hydrothermal process, while The hydrothermal process will inevitably cause sulfur and graphene to be suspended in water without forming a composite structure. Even if the two are composited together, sulfur will only adhere to the surface of graphene, resulting in a low real sulfur load. Because the initial capacity is high, but the capacity declines quickly, it cannot effectively solve the problems of low active material loading and low active material utilization in the existing lithium-sulfur battery cathode materials, and it is difficult to achieve the discharge stability of lithium-sulfur batteries

More importantly, the patent does not modify the structure of graphene. Graphene still maintains the original layer structure. During the drying process, the graphene layers will inevitably be stacked again, reducing its specific surface area, and it is difficult to solve the lithium-sulfur problem. The volume expansion effect of the battery

In addition, the layer-shaped graphene structure is difficult to effectively inhibit the diffusion of sulfur, and the energy barrier of the stacked graphene structure is relatively high, and the difficulty for sulfur to enter the graphene structure is correspondingly increased, making it difficult to form an effective load for sulfur.

(b) A large number of studies have shown that graphene has excellent mechanical properties, thermal conductivity and electrical conductivity. After being combined with sulfur, it can improve the electrochemical performance of lithium-sulfur batteries, but the structure of carbon-sulfur composites will directly affect lithium-sulfur batteries. The conductivity of the positive electrode material and the ability to suppress the effect of electrode volume expansion

This patented technology adopts the in-situ sulfur doping method, which is limited by the different reaction energy levels required in different regions during the graphene hydrothermal reduction process.

The graphene oxide prepared by the improved Hummers method does not have a uniform number of layers, usually ranging from 2 to 20 layers. In the hydrothermal process, the number of oxygen-containing groups contained in different layers of graphene oxide must also be different. This leads to the fact that during the reaction process, graphene with more layers requires more energy, and graphene with fewer layers requires less energy. Therefore, during the in-situ sulfur doping process, sulfur loading will occur in different regions. The inhomogeneous phenomenon leads to structural defects in the carbon-sulfur composite material, and some areas of sulfur are exposed on the surface of graphene, which reduces the conductivity of the positive electrode material

In summary, the lithium-sulfur battery cathode material prepared by this patent has a low and uneven loading of sulfur, and the capacity drops rapidly, which cannot effectively solve the problem of low active material loading and utilization in the existing lithium-sulfur battery cathode materials. The problem of low efficiency and obvious volume expansion effect and poor conductivity

[0006] The fundamental defect in the existing technology CN201610671807.7 in the process of preparing the positive electrode sheet of the foamed graphene lithium-sulfur battery is that the structural modification of graphene in this patent is through the porosity of the foamed nickel material, which is used as a template to prepare porous graphite Sulfur-carbon recombination is completed by smearing sulfur powder for heat treatment. Not only does the prepared foamed graphene have structural defects, but also the good recombination of sulfur and graphene cannot be achieved by using the smearing method, resulting in uneven distribution of sulfur, The effective loading capacity of graphene to sulfur is not high, and the conductivity of the cathode material is poor, which does not solve the shortcomings of low sulfur loading, poor conductivity, and obvious shuttle effect of the cathode material of lithium-sulfur batteries

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