Three-dimensional graphene-hollow carbon sphere/sulfur composite material and its preparation method and application in lithium-sulfur batteries

Abstract

The invention discloses a three dimensional graphene / hollow carbon sphere / sulfur composite material, a preparation method thereof, and an application in lithium-sulfur batteries. The three dimensional graphene / hollow carbon sphere / sulfur composite material comprises nanometer elemental sulfur and a three dimensional graphene-hollow carbon sphere nano-compound, and the nanometer elemental sulfur is distributed in the three dimensional graphene-hollow carbon sphere nano-compound. The preparation method comprises the following steps: dispersing the three dimensional graphene-hollow carbon sphere nano-compound in an alcohol and water mixed solvent to obtain a suspension; and adding an aqueous solution of Na2S.9H2O and Na2SO3 into the suspension, adding an acidic solution, and reacting to obtain the three dimensional graphene / hollow carbon sphere / sulfur composite material. The composite material has the advantages of high specific capacity, stable cycle performances, and excellent rate performance and coulombic efficiency, the preparation method has the advantages of simplicity, convenience and good effect, and the composite material can be applied in the preparation of lithium-sulfur battery positive electrode materials.

Description

technical field [0001] The invention relates to the field of nano-carbon materials and their preparation, in particular to a three-dimensional graphene-hollow carbon sphere / sulfur composite material, its preparation method and its application in lithium-sulfur batteries. Background technique [0002] Secondary batteries with high energy density and low cost have promising applications in portable electronic devices, electric vehicles, and smart grids. Lithium-sulfur batteries have high theoretical specific capacity (1672mAh / g) and energy density (2600Wh / kg), which are several times that of ordinary lithium-ion batteries. In addition, sulfur elemental resources are abundant, cheap, and environmentally friendly. These remarkable advantages make lithium-sulfur batteries regarded as one of the most promising power sources for next-generation electric vehicles. [0003] At present, the main problems that restrict the practical application of lithium-sulfur batteries are as foll...

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Problems solved by technology

[0003] At present, the main problems that restrict the practical application of lithium-sulfur batteries are as follows: (1) The conductivity of sulfur element is poor (only 5×10 -30 S / cm), it needs to be mixed with a large amount of conductive agent, which seriously reduces the utilization rate of sulfur and the rate performance of the battery; (2) the long-chain polysulfide lithium (Li 2 S x , x=3~8) dissolved in the electrolyte, and "shuttle" back and forth between the positive and negative electrodes, resulting in low Coulombic efficiency and reversible capacity; (3) short-chain polysulfide lithium (Li 2 S. Li 2 S 2 ) Form insoluble deposits on the surface of the positive electrode material, resulting in a decrease in electrochemical activity and a decrease in cycle performance; (4) Large volume changes during the cycle cause the pulverization and shedding of the active material

They are all good carriers for lithium-sulfur battery cathode materials with important application prospects, but each has its own shortcomings: the electronic conductivity of hollow carbon spheres is not as good as that of graphene, the pore structure of graphene is not as rich as that of hollow carbon spheres, and graphene has excellent electrical conductivity but There are problems of dissolution and shuttling of lithium polysulfide when it is used alone as a positive electrode material

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