Researchers in have shown that a lithium-sulfur (Li-S) battery with a reduced graphen oxide (rGO) -coated separator exhibits much smaller impedance and much better electrochemical performance than cells with an uncoated separator. After coating with rGO, the initial discharge capacity can be as large as 1067 mAh g−1 at 0.2 C; the cell can retain 878 mAh g−1 after 100 cycles; and the discharge capacity can reach 710 mAh g−1 even at 2 C.
The team attributed the significant performance enhancement to the bi-functionality of rGO; the rGO coating layer has a unique porous structure, high conductivity and various kinds of functional groups, which can not only effectively prevent the diffusion of polysulfide through the separator, but also significantly increase the conducting surface between cathode and separator.
It is promising to use rGO-based slurry to continuously produce large-scale, low-cost, and bi-functional rGO coated separator for high-performance Li-S batteries.—Lin et al.
There are multiple ways to produce graphene: micro-mechanical exfoliation of highly ordered pyrolytic graphite; epitaxial growth; chemical vapor deposition; and the reduction of graphene oxide (GO). GO has two important characteristics, noted Pei and Cheng in 2012 paper in the journal Carbon:
it can be produced using inexpensive graphite as raw material by cost-effective chemical methods with a high yield; and
it is highly hydrophilic and can form stable aqueous colloids to facilitate the assembly of macroscopic structures by simple and cheap solution processes, both of which are important to the large-scale uses of graphene.
Different reduction processes result in different properties of reduced GO (rGO), which in turn affect the final performance of materials or devices composed of rGO.
Wei Lin, Yuanfu Chen, Pingjian Li, Jiarui He, Yan Zhao, Zegao Wang, Jingbo Liu, Fei Qi, Binjie Zheng, Jinhao Zhou, Chen Xu, and Fei Fu (2015) “Enhanced Performance of Lithium Sulfur Battery with a Reduced Graphene Oxide Coating Separator” J. Electrochem. Soc. 162(8): A1624-A1629; doi: 10.1149/2.0891508jes
Songfeng Pei, Hui-Ming Cheng (2012) “The reduction of graphene oxide,” Carbon, Volume 50, Issue 9, Pages 3210-3228 doi: 10.1016/j.carbon.2011.11.010