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Lithium doped N,N-dimethyl pyrrolidinium tetrafluoroborate organic ionic plastic crystal electrolytes for solid state lithium batteries

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journal contribution
posted on 01.01.2011, 00:00 authored by Liyu Jin, Patrick HowlettPatrick Howlett, Jim Efthimiadis, Mega KarMega Kar, D MacFarlane, Maria ForsythMaria Forsyth
The organic ionic plastic crystal material N,N-dimethyl pyrrolidinium tetrafluoroborate ([C1mpyr][BF4]) has been mixed with LiBF4 from 0 to 8 wt% and shown to exhibit enhanced ionic conductivity, especially in the higher temperature plastic crystal phases (phases II and I). The materials retain their solid state well above 100 °C with the melt not being observed up to 300 °C. Interestingly the conductivity enhancement is highest with the lowest level of LiBF4 addition in phase II, but then the order of enhancement is reversed in phase I. In all cases, a conductivity drop is observed at the II → I phase transition (105 °C) which is associated with increased order in the pure matrix, as previously reported, although the conductivity drop is least for the highest LiBF4 amount (8 wt%). The 8 wt% sample displays different conductivity behaviours compared to the lower LiBF4 concentrations, with a sharp increase above 50 °C, which is apparently not related to the formation of an amorphous phase, based on XRD data up to 120 °C. Symmetric cells, Li/OIPC/Li, were prepared and cycled at 50 °C and showed evidence of significant preconditioning with continued cycling, leading to a lower over-potential and a concomitant decrease in the cell resistivity as measured by EIS. An SEM investigation of the Li/OIPC interfaces before and after cycling suggested significant grain refinement was responsible for the decrease in cell resistance upon cycling, possibly as a result of an increased grain boundary phase.

History

Journal

Journal of materials chemistry

Volume

21

Issue

27

Pagination

10171 - 10178

Publisher

Royal Society of Chemistry

Location

Cambridge, U. K.

ISSN

0959-9428

eISSN

1364-5501

Language

eng

Publication classification

C1 Refereed article in a scholarly journal

Copyright notice

2010, The Royal Society of Chemistry.