Researchers at Hunan University, China, have developed a new strategy to suppress the diffusion of polysulfides into the electrolyte in Li-Sulfur batteries, resulting in improved performance.
As described in a paper in the Journal of Power Sources, the research tea used hydrophilic carbon paper anchored by hierarchically porous cobalt disulfides as an interlayer for capturing polysulfides through physical absorption and chemical bonding. The sulfur-graphene composite with a sulfur content of 70.5% delivers a high initial capacity of 1239.5 mAh g−1 at 0.2 C and retains a reversible capacity of 818 mAh g−1 after 200 cycles.
|The schematic diagram of CoS2/CP capturing Li2S. Ma et al. Click to enlarge.|
… in the progress of realizing the commercialization of Li-S battery, two main critical technical issues lead to low discharge capacity and short cycle life: the shuttling behavior of the dissolved polysulfides as well as the serious volume expansion of sulfur electrode. So far, various effective strategies are utilized to promote the discharge capacity and cycling lifetime. As one of the strategies, inserting a porous interlayer between the separator and sulfur electrode is widely applied to address the above-mentioned issues.
… We, herein, prepared an interlayer of the carbon paper anchored by hierarchical porous CoS2 (CoS2/CP). It was used to encapsulate the polysulfides and alleviate the volume expansion in the sulfur-reduced graphene oxide (S/rGO) cathode.—Ma et al.
The hierarchical porous CoS2/CP interlayer offers three main benefits, the team said:
It can act as the upper current collector, promote electron transport and provide a parallel buffering space between the CoS2/CP interlayer and Al foil for mitigating severe volume expansion. Furthermore, the existence of the upper current collector facilitates the dissolved polysulfides to capture the electrons quickly and enhance the utilization of the inner sulfur particles of the S/rGO cathode.
The hierarchical pore structure prolongs the path length of polysulfides arriving at the lithium anode, reducing impairment.
The polar Co-S bond can interact strongly with Li-S bond of Li2Sn/Li2S—i.e., tt is a highly effective approach for chemically bonding with Li2Sn/Li2S.
After two cycles’ at 0.1 C, a cell with an S/rGO electrode with CoS2/CP interlayer delivered the higher initial capacity of 1239.5 mAh g-1 in contrast to 950.0 mAh g-1 for S/rGO electrode with just a CP interlayer and 914.4 mAh g-1 for the bare S/rGO electrode.
Zhaoling Ma, Zhen Li, Kui Hu, Dongdong Liu, Jia Huo, Shuangyin Wang (2016) “The enhancement of polysulfide absorption in LiS batteries by hierarchically porous CoS2/carbon paper interlayer”, Journal of Power Sources, Volume 325, Pages 71-78 doi: 10.1016/j.jpowsour.2016.04.139