Improving the performance of lithium-sulfur batteries using conductive polymer and micrometric sulfur powder
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In this study, a conductive polymer, poly(3,4-ethylenedioxythiophene) or PEDOT, was used as binder in the sulfur electrode to study electrochemical performance of lithium–sulfur (Li–S) batteries. PEDOT-based sulfur electrode was compared with that of polyvinylidene difluoride binder based sulfur electrode. Different particle size sulfur materials including commercial micrometric sulfur particles and synthesized colloidal nanometric sulfur powders were chosen as active materials to study the impact of particle size on the cell performance. Different electrolytes including lithium bis(trifluoromethanesulfonyl)imide in polyethylene glycol dimethyl ether (PEGDME) or 1,3-dioxolane-dimethoxy ethane were used in the Li–S batteries to investigate the impact of electrolyte on cell performance. The PEDOT and micrometric sulfur based electrode with PEGDME electrolyte had the best cycle performance, which showed a capacity retention of 68% and specific capacity of 578 mAh/g after 100 cycles. The increased conductivity by conductive polymer and the high viscosity of PEGDME play important roles in the improvement of cycle performance.
I. INTRODUCTION
Due to environmental concerns, it becomes more and more important to find alternative energy sources beyond fossil fuels with increasing demand of energy. Lithiumion batteries (LIB) have drawn significant research attention due to their unique advantages of relatively high energy densities. Applications of LIB have been extended from consumer electronics to large-scale grid energy storage. However, the energy density of currently existing LIB remains insufficient to meet the requirements for applications in electric vehicles and hybrid electric vehicles, and thus it is desirable to develop much higher energy density rechargeable batteries with low cost.1–3 There has been significant progress in the development of high energy density anode materials such as Si-based alloy etc. over the recent years.4–8 However, the low capacity of cathode materials is still one of the major obstacles for developing high-performance batteries. Sulfur has been considered as one of the promising candidates of such cathode materials due to its high theoretical capacity (1675 mAh/g) and its natural abundance. Despite the above advantages, there are still many challenges in developing a practical lithium–sulfur battery for commercialization. As known so far that the problems of lithium–sulfur batteries include: (i) very poor conductivity of sulfur (10 16 S/m at 293 K); (ii) large volumetric a)
Address all correspondence to this author. e-mail: [email protected] b) These authors contributed equally to this work. DOI: 10.1557/jmr.2014.85 J. Mater. Res., Vol. 29, No. 9, May 14, 2014
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expansion upon lithiation (80%); (iii) dissolution of the intermediate polysulfides during charge–discharge processes. 9,10 These problems result in fast capacity fading and low Coulombic efficiency and therefore result in poor cycle performance of lithium–sulfur cells. Considerable effo
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