Correlation study of solid phase conversion sulfur electrode:Lithium sulfur batteries have become a new type of energy storage system with high theoretical energy density, extensive source of raw materials and low cost. Despite years of development, various novel structural sulfur composite positive electrode materials, various transition metals related chemical adsorption intermediate or electrochemical catalysts, such as rain, spring bamboo shoots, inhibit the notorous multi-sulfide shuttle, but lithium sulfur The practical progress of the battery is still very slow. A Xinping Professor I once found that only a large battery in the laboratory can only be used to cycle a few weeks or even can't charge and discharge. A Xinping Professor Team believes that from the perspective of thermodynamics, as long as the electrochemical mechanism of polysulfide in the lithium sulfur battery is present, the shuttle effect cannot be fundamentally inhibited. The utility process of lithium sulfur batteries can only be truly promoted by converting lithium sulfur battery electrochemical oxidation mechanisms to solid phase conversion mechanisms.
Fig. 2 is a schematic diagram of the inner SEI layer of sulfur particles in the surface of the sulfur particles in the carbonate-ether culechant electrolyte
Previous studies have found that polysulfides do not dissolve in many high viscosity, high concentrations or some room temperature ionic liquid electrolytes, and their electrochemical reactions are ideal for solid phase conversion mechanisms. However, these electrolytes are either infiltrating or less ion conductivity, so that the utilization rate of sulfur active materials with poor electrical conductivity is low. Combined with the previous research work, Akinopa team developed a carbonate-ether electrolytic solution to achieve sulfur positive electrode solid phase conversion reaction under high sulfur loading [3]. In this 1 M Litfsi IN DOL / DME (1: 1) + 10% VC electrolytic liquid system, the ether electrolyte is first dissolved in the first few cases of electrochemical circulation to generate a polysulfide intermediate. A nucleophilic reaction occurs between the polysulfide intermediate and the vinyl carbonate to form a layer of dense SEI layer on the surface of sulfur particles. This layer of dense SEI layer having high ion conductivity can be tightly wrapped in sulfur particles to contact the electrolytic solution during the later electrochemical cycle, so the active material sulfur does not continue to occur, the electrochemical mechanism is followed. Solid phase conversion reaction. Under this solid phase conversion reaction mechanism, the S / C positive electrode can still achieve the discharge ratio capacity of up to 1100 mAh / g at a current density of 100 mA / g, and the capacity retention ratio is as high as 88%, and The average Turning efficiency after the weekly dissolution process is close to 100%.
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