Functionalized Ionic Liquid-Based Electrolytes for Li-Ion Batteries
Ionic liquids (ILs) are molten salts with an immense potential as an electrolyte in battery which fulfills the two most demanding aspects, negligible volatility, and non-flammability along with low melting temperature affecting their wide range applicability. Along with these aspects, ILs need suitable functionalization of the chosen cationic and/or anionic component for high stability within the working potential of the battery and suitable ionic conductivity. The chemistry of the substituent groups and the interaction between this cation and anion of an ionic liquid are the key to fine-tune the electrolyte. The present chapter deals with the functionalization of alkoxy (R–O–R) and siloxy (Si–O–Si) groups as substituents over the imidazolium cation. This modified cation was associated with an electronically diffused anion, N, N- bis(trifluoromethane)sulfonimide (TFSI, CF3SO2)2NH) to control the extent of cluster formation prevalent in the presence of high concentration of lithium-ion (Li+, 1 mol/kg solvent). This cluster formation regulates the viscosity which in turn controls the obtainable ionic conductivity essential for good charge-discharge characteristics. Another issue of high-energy electrodes reacting slowly with the ionic liquid electrolyte and requiring a long time for a stable solid electrolyte interface formation was addressed by using an organic additive, namely, propylene carbonate (PC, C4H6O3). The concept of a functionalized electrolyte mixture comprising of an ionic liquid, organic additive, and Li-ion source is pursued in depth, and its impact over the various parameters of the electrolyte was analyzed. The probable impact of these ionic liquid mixtures in the battery electrolyte was assessed both physical and electrochemical characterization. The functional applicability was finally tested by performing charge-discharge cycling in a compiled battery consisting of a graphite (C) anode and lithium cobalt(III) oxide (LiCoO2) cathode separated by the ionic liquid mixture soaked separator.
KeywordsLi-ion battery Battery electrolyte Functionalized ionic liquid Battery testing
This research is supported by the Department of Atomic Energy (DAE), India (2013/37C/57/BRNS). Dr. Tharamani C. Nagaiah thanks the Department of Science and Technology (DST) for the Ramanujan Fellowship (SR/S2/RJN-26/2012). Aarti Tiwari thanks IIT Ropar for Fellowship.
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