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Preparation and Electrochemical Properties of Sulfur-based Cathode for Lithium-sulfur Battery

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Tutor: LiYaJuan
School: Central South University
Course: Chemical Engineering and Technology
Keywords: lithium-sulfur battery,sulfur/expanded graphite,thermaltreatment,Ni foam
CLC: TM912
Type: Master's thesis
Year:  2013
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Abstract:
Lithium-sulfur battery is one of the most valuble chemical power sources due to its high theoretical power density, earth abundant resources, environmental friendliness and low cost. Improving the electrical conductivity of the sulfur electrode and optimizing its structure are effective methods to solve the problems of poor cycling ability and low utilizaiton of active material in lithium-sulfur battery. Expanded graphite (EG), which has3D-layered structure, was used to fabricate sulfur/expanded graphite (SEG) composite in this work. In addition, the influence of the Ni foam current collector on the electrical properties of lithium-sulfur battery was investigated, and the reaction mechanism was discussed. The main contents are shown as follows.SEG composite was designed and prepared, and the effects of preparation method, thermal treating time, sulfur loading, and thermal treating temperature on the performance of materials were investigated. The results revealed that the electrochemical performance of SEG composite prepared by the ball milling-thermal treating method was superior to that of the composite synthesised by the ball milling method. The SEG composite with50wt%S prepared with two thermal treatment stages (150¡æfor6h,300¡æfor10h) delivered the initial discharge capacity of732mAh¡€g-1at0.2C, and maintained about500mAh¡€g-1after50cycles. Compared with the sublimed S cathode, the improved electrochemical performance of the SEG cathode was attributed to the introduction of EG acted as micro current collectors to improve the conductivity of the cathode material, confine the diffusion of dissolved polysulfides, and maintain the stable structure of the cathode matrix.The electrochemical properties of sulfur electrodes with two different current collectors, Ni foam and stainless steel mesh, were investigated. When the sulfur electrode with Ni foam current collector was cycled between1.0V and2.7V, a new pair of redox peaks at1.35/2.0V was found, which was caused by the redox reaction of NiS. The research demonstrated that Ni from the Ni foam current collector was transformed into NiS, resulting in a great improvement of the specific capacity, cycle life, and the Coulombic efficiency. This research finding was of great significance for the lithium-sulfur battery with Ni foam current collector.
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