For the further development of lithium ion batteries, it is essential to replace the liquid electrolytes by solid ones because they are nonflammable and more easily processable. Up to now, the solid electrolytes have a lower ionic conductivity. A new approach is the use of liquid crystalline compounds. Liquid crystals having ion conducting segments can transport ions efficiently as segregation leads to the formation of nanoscale ion pathways.We investigated liquid crystalline molecules with a perfluorinated aromatic ring as the mesogenic core and a cyclic carbonate as the ion conductive moiety. Small-angle X-ray scattering and polarized optical microscopy revealed that they form the smectic phase (Figure). Spontaneous macroscopic alignment was observed when the substances were cooled from the isotropic melt. The influence of lithium salt concentration and the length of the alkyl chain on the alignment of the molecules and the layer spacing were investigated. These findings were compared with anisotropic conductivity measurements in the smectic as well as in the isotropic phase to get new insights into the conductivity mechanism. The conductivity parallel to the layer plane was significantly higher than perpendicular and is one of the best reported for liquid crystals with propylene carbonate fragments.

Structure and conductivity of liquid crystals having carbonate units for the use as electrolytes in lithium-ion batteries

248th National Meeting (2014)

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