N-Methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide-based organic electrolyte for high performance lithium–sulfur batteries

Development of lithium–sulfur (Li–S) batteries has suffered from insufficient capacity and poor cycle-life. One of the reasons for these drawbacks is loss of active material, which is associated with the rapid diffusion of highly soluble lithium polysulfides formed as intermediates of discharge products in organic electrolytes, resulting in internal shuttling of lithium polysulfides. The diffusion of lithium polysulfides is determined largely by the physicochemical properties of electrolytes. Therefore, design of the physicochemical properties of the electrolyte to restrain the internal shuttling is vital to promote high performance for Li–S batteries. Here we present a newly designed room temperature ionic liquid (RTIL)-based organic electrolyte for Li–S battery. Our electrolyte provides a trade-off between solubility and diffusion rate of lithium polysulfides by mixing very different physicochemical properties of two solvents: high lithium polysulfide solubility of 1,2-dimethoxyethane (DME), and high viscosity of N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13-TFSI). An adequate composition ratio of mixed PP13-TFSI/DME afforded large capacity, high Coulombic efficiency, improved capacity retention, and suppressed internal shuttling.

Graphical abstractA newly designed room temperature ionic liquid (RTIL)-based organic lithium electrolyte providing a trade-off between solubility and diffusion rate of lithium polysulfides by mixing N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13-TFSI) and DME with an optimal composition ratio was effectively employed in the Li–S battery, which achieved a large capacity of ∼1000 mA h g−1 at 0.2 C, a high Coulombic efficiency of almost 100%, and an improved capacity retention of ∼90% over 50 cycles in addition to slow internal shuttling.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Design of PP13-TFSI/DME electrolyte for Li–S batteries. ► Suppression of internal shuttling using PP13-TFSI/DME. ► Achievement of reliable performance of Li–S batteries with PP13-TFSI/DME.