Synthesis and evaluation of a novel pyrrolidinium-based zwitterionic additive with an ether side chain for ionic liquid electrolytes in high-voltage lithium-ion batteries.

Ionic liquids (ILs) containing zwitterions were studied as electrolytes for lithium-ion batteries. The effect of a pyrrolidinium zwitterion with a long ether side chain on the thermal and electrochemical properties of an IL and the charge/discharge properties of Li/LiCoO 2 , Li/LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC), and graphite/Li cells with IL/zwitterion electrolytes was investigated. The melting temperature of the IL-based electrolyte composed of N -methyl- N -methoxymethylpyrrolidinium bis(fluorosulfonyl)amide ([Pyr 1,1O1 ][FSA]) and lithium bis(fluorosulfonyl)amide (LiFSA) with 3-(1-(2-(2-methoxyethoxy)ethyl)pyrrolidin-1-ium-1-yl)propane-1-sulfonate (OE2pyps) as the zwitterionic additive was about −18 °C. The electrochemical window of [Pyr 1,1O1 ][FSA]/LiFSA/OE2pyps was over 5 V vs. Li/Li + . Li|electrolyte|LiCoO 2 cells containing the [Pyr 1,1O1 ][FSA]/LiFSA/OE2pyps electrolyte system exhibited high capacity values in the cut-off voltage range of 3.0–4.3 V, even after 50 cycles. Moreover, increases of interfacial resistance between the electrolyte and cathode during cycling were suppressed. Li|electrolyte|NMC cells containing this electrolyte system also exhibited high capacities in a wide cut-off voltage range of 3.0–4.6 V, even after 50 cycles. In the cyclic voltammograms of cells employing a graphite electrode, the intercalation/deintercalation of lithium ions was observed between 0 and + 0.4 V vs. Li/Li + . Further, graphite|electrolyte|Li cells containing [Pyr 1,1O1 ][FSA]/LiFSA/OE2pyps exhibited stable charge/discharge cycle behavior over 5 cycles. [ABSTRACT FROM AUTHOR]