| 초록 |
Lithium ion batteries(LIB) are the most widely used rechargeable battery for portable devices because of their high energy density (387 Wh kg-1) and long cycle life. Nevertheless, the energy density of LIBs is insufficient to meet the demands for grid energy storage system or electrical vehicles. Therefore, the lithium-sulfur battery(LSB) has been researched extensively as the most promising system for the alternative rechargeable battery. Because of the high theoretical specific capacity of elemental sulfur (1675 mAh g-1), LSB has the high theoretical energy density (2,500 Wh kg-1) which is ~7 times larger than the energy density of the current LIBs. In spite of the considerable promises, there are multiple challenges to be solved. First, the capacity fades during cycling originated from the “shuttling effect.” Second, the sulfur has an intrinsic poor electrical conductivity. Third, the volume of the sulfur are expanded during cycles. In order to solve those problems, researchers have studied sulfur combined with carbon materials. The carbon materials can give a good electrical conductivity, accommodate the polysulfides, and relax the volumetric expansion with flexibility of carbon. Many kinds of sulfur-nano carbon design such as porous carbon, graphene, and CNTs have shown significant improvement of LSB. In this study, we developed a sulfur electrode which is focused on electrode design. Core-shell nanofibers composed of electrospun hollow carbon nanofiber and sulfur composite were fabricated. The composite was designed for cathode material that the carbon gives an excellent electrical conductivity to the surface of the sulfur by encapsulating the sulfur. It made the most part of the sulfur be utilized and realized high specific discharge capacity. Moreover, encapsulating the sulfur with carbon prevented the polysulfide dissolution in the liquid electrolyte. From a structural point of view, the resulting intertwined nanofibers showed a porous structure. The highly porous structure can accommodate electrolyte effectively and offer abundant electrochemical reaction sites with large surface area. The excellent performance of LSB was demonstrated with these encapsulated sulfur cathode material from hollow carbon nanofiber-sulfur. |
