Among the emerging energy storage methods, lithium-sulfur battery (LiS) has drawn plenty of attentions due to its high theoretical energy density (2600 Wh kg^-1),¹ economical cost and environmental benignity. Nevertheless, the insulating nature of sulfur and notorious polysulfides shuttling result in a low sulfur utilization and short cycling life.² To address these problems, carbon material has been confirmed as an ideal sulfur host to promote LiS’s performance because of their low cost, high conductivity and controllable structure such as carbon spheres, carbon nanotube/fibers and carbon nanosheets. For example, one-dimensional carbon nanotube can increase the sulfur utilization by providing better electrical conductivity. However, its “open-to-electrolyte” structures cannot effectively prevent shuttling effect.³ As for zero-dimension carbon materials, core/yolk shell carbon spheres in particular, are less capable of establishing conductive networks, which in turns, compromise the sulfur utilization and rate capability.⁴ Thus, it is of great necessity to develop three-dimensional (3D) carbon materials with multiple functions in order to achieve high-performance lithium-sulfur batteries.

Along this line, we prepared a three-dimensional carbon nanosheets modified carbon nanofiber (3DCNF) as high porosity sulfur host. After decorated with vertically aligned carbon nanosheets, the surface area of pristine carbon nanofiber was dramatically increased from 30 m²/g to 500 m²/g due to the expanded dimension. Although both 1D nanofiber and 2D nanosheets cannot effectively prevent polysulfides shuttling by themselves, the delicate combination of them endows new functions, where 3D carbon hybrid is capable of accommodating sulfur expansion and deterring polysulfides dissolution by the hierarchical porous structure and interconnected carbon nanosheets. At the same time, the 3D porous carbon nanofiber can also form conductive network that allows rapid electron transfer. With the structural advantages, the 3DCNF and sulfur composite delivered a capacity as high as 1266, 977 mAh/g at 0.1 and 0.5 C, respectively. After 500 cycles at 0.5 C, it still retains a capacity of 607 mAh/g (0.07% capacity fading per cycle), exhibiting excellent cycling capability.

Reference

1. M. K. Song, E. J. Cairns and Y. Zhang, Nanoscale, 2013, 5, 2186-2204.
2. Y. Yang, G. Zheng and Y. Cui, Chem. Soc. Rev., 2013, 42, 3018-3032.
3. X. Liang, Z. Wen, Y. Liu, H. Zhang, J. Jin, M. Wu and X. Wu, J. Power Sources, 2012, 206, 409-413.
4. Y. J. Hong, J.-K. Lee and Y. Chan Kang, J. Mater. Chem. A, 2017, 5, 988-995.