Preparation And Eletrochemical Characterization Of The Porous Sulfur Cathode Using A Gelatin Binder In Lithium-Sulfur Batteries

Elemental sulfur is a kind of most promising cathode material for the next generation lithium batteries, due to the high specific capacity, abundant resources, and low toxicity. However, the actual application of a rechargeable lithium-sulfur battery still has a number of problems to overcome, such as low active-material utilization, poor cycle performances. In this thesis, our researches were carried out from the sight of the selection of binder and the design of the cathode structure, the preparation and electrochemical performances of a novel porous sulfur cathode with gelatin binder was systematically studied, which opened up a new field for scientific research on the development of rechargeable lithium-sulfur battery.Firstly, gelatin, a natural biological macromolecule, was successfully used as a new binder in the fabrication of well dispersed sulfur cathode for the first time in this thesis, and the electrochemical performances of this sulfur cathode was studied with lithium anode and1M LiC104/DME+DOL (V/V=1/1) as electrolyte. The results showed that the gelatin binder had multifunctional effects on the sulfur cathode:it not only functioned as a highly adhesive agent and an effective dispersion agent for the cathode materials, but also an electrochemically stable binder which did not swell in the electrolyte, thus can keep cathode stable. The gelatin-sulfur cathode achieved a high initial capacity of1132mAh g-1, and remained at a reversible capacity of408mAh g-1after50cycles, all of which were better than that of the PEO-sulfur cathode under the same conditions.Secondly, the studies on the products of elemental sulfur cathode at different stage during the charge-discharge process showed that gelatin binder could enhance the redox reversibility of sulfur cathode, which was compared with the PEO binder. It is suggested that the reducing reaction of elemental sulfur can be slow down during the first discharge and Sg could be reformed by charging during the first charge-discharge process, thus, the discharge capacity and cycle performance of sulfur cathode can be improved. This result has not been reported before.Finally, a creative design of novel porous sulfur cathode with gelatin binder was prepared the by using a freezing-drying method for the first time. The diameter of pores are between200～500nm. This porous structure provides channels for electrolyte infiltration and then facilitates ion diffusion. The test results showed that the porous structure is in favor to enhance the electrochemical performances of sulfur cathode. This porous sulfur cathode had a high initial capacity of1235mAh g-1and a high reversible capacity of 626mAh g-1after50cycles, both of which are higher than that of the normal sulfur cathodes with compact structures.