Ionic liquid electrolyte for lithium metal batteries: physical, electrochemical, and interfacial studies of N-Methyl-N-butylmorpholinium Bis(fluorosulfonyl)imide

George Lane, Paul Bayley, Bronya Clare, Adam Best, Douglas Macfarlane, Maria Forsyth, Anthony Hollenkamp

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The ionic liquid (IL) N-methyl-N-butylmorpholinium bis(fluorosulfonyl)imide (C(4)mmor FSI) is examined from physical and electrochemical perspectives. Pulsed field gradient NMR spectroscopy shows that ion diffusivities are low compared with similar, non-ethereal ILs. Ionicity values indicate that above room temperature, less than 50 of ions contribute to conductivity.Lithium cycling in symmetrical cells using a C(4)mmor FSI-based electrolyte is best demonstrated at elevated temperatures. Specific capacities of 130 mAh g(-1) are achieved in a Li-LiFePO4 battery at 85 degrees C. FT-IR spectroscopic investigations of lithium electrodes suggest the presence of alkoxide species in the solid electrolyte interphase (SEI), implying a ring-opening reaction of C(4)mmor with lithium metal. In contrast, the SET derived from N-methyl-N-propylpiperidinium FSI lacks the alkoxide signature but shows signs of alkyl unsaturation, and the activation energy for Li+ transport through this SEI is slightly lower than that for the C(4)mmor-derived SEI Our detailed findings give insight into the capabilities and limitations of rechargeable lithium metal batteries utilizing a C(4)mmor FSI electrolyte.
Original languageEnglish
Pages (from-to)21775 - 21785
Number of pages11
JournalJournal of Physical Chemistry C
Issue number49
Publication statusPublished - 2010

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