Molybdenum diselenide modified nitrogen-doped graphene composite material and preparation method thereof, and nitrogen-doped graphene-based lithium-sulfur battery positive electrode material

Abstract

The invention provides a molybdenum diselenide / nitrogen-doped graphene composite material. The composite material comprises nitrogen-doped graphene and a molybdenum diselenide nanosheet compounded on a nitrogen-doped graphene sheet layer. The electrochemical performance of the lithium-sulfur battery is improved through the synergistic effect of heteroatom doping and molybdenum diselenide modification, nitrogen atoms are doped with graphene, transmission and exchange of substances in the charging and discharging process of the battery are enhanced, meanwhile, the electron transmission capacity of the surface of the positive electrode is improved, the utilization rate of active substances is increased, and meanwhile, the electrochemical performance of the lithium-sulfur battery is improved. The shuttle effect of lithium polysulfide is inhibited to a certain extent; molybdenum diselenide is adopted for modification and serves as a chemical adsorption site and a catalytic activity site of lithium polysulfide, rapid conversion of polysulfide ions is catalyzed, kinetic reaction is accelerated, the shuttle effect is inhibited, and then the cycle performance of the lithium-sulfur battery positive electrode material is obviously improved. Meanwhile, the composite material has specific layered morphology and microstructure, and the acting effect of the composite material is further improved.

Description

technical field [0001] The invention belongs to the technical field of positive electrode materials for lithium-sulfur batteries, and relates to a molybdenum diselenide / nitrogen-doped graphene composite material and a preparation method thereof, and a nitrogen-doped graphene-based battery positive electrode material, in particular to a molybdenum diselenide modified molybdenum diselenide Nitrogen-doped graphene composite material and preparation method thereof, nitrogen-doped graphene-based lithium-sulfur battery cathode material. Background technique [0002] With the continuous consumption of fossil energy, the energy crisis we are facing and the environmental pollution caused by the use of fossil energy are becoming more and more serious. It is necessary to develop new clean energy, such as wind energy, solar energy, and geothermal energy. However, the utilization of clean energy is inseparable from electrochemical energy storage devices. Safe, efficient, and environment...

AI Technical Summary

Problems solved by technology

[0003] However, lithium-sulfur batteries also have their own problems: (1) the insulation of the active material, the conductivity of sulfur is only 5×10 -30 S cm -1 , the low conductivity leads to a large difference between the actual specific capacity and the theoretical specific capacity, and it is necessary to add conductive carbon as a conductive substance

(2) The shuttle effect is relatively serious. The lithium-sulfur battery is a complex redox reaction, and the intermediate product lithium polysulfide will be dissolved in the electrolyte. Due to the solubility gradient, the intermediate product will move from the positive electrode to the negative electrode. Migration, on the one hand, causes the loss of the active material sulfur, on the other hand, the polysulfides migrating to the negative electrode will have an uncontrolled redox reaction with the metal lithium sheet, which reduces the Coulombic efficiency and affects the electrochemical performance; (3 ) The problem of volume expansion caused during the discharge process is more serious, because the density of sulfur is 2.07g cm -3 , while the density of the discharge product lithium sulfide is only 1.66g cm -3

Although these four types of materials can inhibit the dissolution, migration and diffusion of polysulfide ions to varying degrees, reducing the Li 2 S 2 and Li 2 The deposition of S on the outer surface of the material improves the utilization rate of the active material sulfur and improves the cycle performance of the lithium-sulfur battery, but it still cannot meet the relevant requirements of the downstream application industry.

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