Ionic Liquid Electrolytes for Lithium–Sulfur Batteries

Abstract

A variety of binary mixtures of aprotic ionic liquids (ILs) and lithium salts were thoroughly studied as electrolytes for rechargeable lithium-sulfur (Li-S) batteries. The saturation solubility of sulfur and lithium polysulfides (Li 2 S m ), the active materials in the Li-S battery, in the electrolytes was quantitatively determined, and the performance of the Li-S battery using the electrolytes was also investigated. Although the solubility of nonionic sulfur was low in all of the electrolytes evaluated, the solubility of Li 2 S m in the IL-based electrolyte was strongly dependent on the anionic structure, and the difference in the solubility could be rationalized in terms of the donor ability of the IL solvent.Dissolution of Li 2 S m in the ILs with strong donor ability was comparable to that achieved with typical organic electrolytes; the strongly donating IL electrolyte did not prevent redox shuttle reaction in the Li-S cells. The battery performance was also influenced by unfavorable side reactions of the anions (such as tetrafluoroborate (BF 4 − ) and bis(fluorosulfonylamide) ([FSA] − )) with polysulfides and by slow mass transport in viscous ILs, even though the dissolution of Li 2 S m into the IL electrolyte was greatly suppressed. Among the IL-based electrolytes, the low-viscosity [TFSA]-based ILs facilitated stable charge/discharge of the Li-S batteries with high capacity and high coulombic efficiency. The unique solvent effect of the ILs can thus be exploited in the Li-S battery by judicious selection of ILs that exhibit high lithium-ion-transport ability and electrochemical stability in the presence of Li 2 S m .

Design and Materialization of Ionic Liquids Based on an Understanding of Their Fundamental Properties

“…117,122 Consequently, solvate ILs are suitable for use as electrolytes in lithium ion batteries [111][112][113][114] and lithium-sulfur batteries. [115][116][117][118][119][120] The most striking and significant findings of our research on solvate ILs are the formation criteria of solvate ILs, 101 the enhanced oxidation stability of coordinating solvents, 95 the low coordinating properties of solvate cations and anions, and their electrode reactions with graphite. 121,122 Figure 8 shows how the anionic structures of lithium salts affect the formation of solvate ILs.…”

“…[115][116][117][118][119][120] The theoretical capacity of the S cathode is ten times greater than that of conventional cathode materials used in current Li-ion batteries. However, Li-S batteries suffer from the dissolution of lithium polysulfides, which are formed by the redox reactions at the S cathode.…”

Li2S nano spheres anchored to single-layered graphene as a high-performance cathode material for lithium/sulfur cells

“…In order to obtain high capacity in cells, it is very important to increase the conductivity of electrode and use an optimized cell composition. In our work, the role of the ionic liquid in the electrolyte is to palliate the high mobility of polysufides and to improve the capacity and rate capability of the cells [51,52]. LiNO 3 is believed to be an effective additive in the electrolyte that not only helps the electrochemical oxidation of Li 2 S, but also prevents polysulfides from contacting the Li anode by generating a protective film on the Li metal anode.…”

Preparation of Micropore-rich High Surface Area Activated Carbon from N-doped Carbon Precursor and its Application to Positive Electrode in Lithium-sulfur Battery

“…These processes mean redox shuttle reactions in a liquid electrolyte and induce a rapid capacity loss. Also, Li polysulfides react with various electrolyte components that are carbonate solvents, 4 bis(fluorosulfonyl)imide (FSI) anion, 5 etc. In order to overcome these problems, there have been some approaches: solvated ionic liquid electrolytes, 6-8 S-polymer composites 9,10 and S-carbon (S-C) composites, 11,12 etc.…”