Researchers from the Beijing Institute of Technology and the Collaborative Innovation Center of Electric Vehicles in Beijing have designed new ionic-liquid-based electrolytes with binary lithium salts to address the issues of rapid capacity fading and low coulombic efficiency in rechargeable lithium-sulfur batteries. The Li–S cells containing this electrolyte system show and initial discharge capacity of 1264.4 mAh g−1, with 911.4 mAh g−1 after 50 cycles with coulombic efficiency of more than 95%.
The new electrolyte contains N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)-imide (Pyr1,2O1TFSI) and tri(ethylene glycol)dimethyl ether (TEGDME) in mass ratio of 7:3, with a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.84 nm) and LiODFB (0.60 nm) mixture with a total molar concentration of 0.4 mol kg−1 as the binary lithium salt.
Although LiODFB as an additive can lead to extremely high viscosity of the electrolyte and inferior performance, the researchers found an optimal combination with LiTFSI.
The researchers attributed the improved performance to the solid-electrolyte interphase (SEI)-forming ability of LiODFB, which protects the Li anode from lithium dendrites and prevents the shuttle phenomenon. A paper on their work is published in the Journal of Power Sources.
Feng Wu, Qizhen Zhu, Renjie Chen, Nan Chen, Yan Chen, Yusheng Ye, Ji Qian, Li Li (2015) “Ionic liquid-based electrolyte with binary lithium salts for high performance lithium–sulfur batteries,” Journal of Power Sources, Volume 296, Pages 10-17 doi: 10.1016/j.jpowsour.2015.07.033