Conformations and vibrations in polymer electrolytes

Sammanfattning: Solvent-free solid electrolytes can be formed by dissolving a salt in a polymer matrix (e.g. poly (ethylene oxide), PEO). Such compounds are of interest due to their proposed use as solid electrolytes in new types of electrochemical devices e.g. all solid-state thin-film lithium polymer batteries for the consumer electronics market.Polymer electrolytes are highly complex materials. The present work has used vibrational spectroscopy in combination with ab initio quantum mechanical calculations to assign vibrational spectra and to study conformational changes in the polymer matrix and the dissolved species.PEO based polymer electrolytes are often multi-phase systems, which is regarded as a major problem since the cations (lithium ions) are conducted only in the amorphous phase, while the crystalline phases can only serve as salt reservoirs. Therefore liquid model compounds, methyl end-capped oligomers of PEO,known as "glymes", have been used to facilitate both the experimental as well as thecomputational part of the investigation.In an ideal polymer electrolyte the cations are conducted by means of the segmental motion of the polymer host while the anions are thought to diffuse freely using free space created in the , polymer matrix. The cation-polymer complex formation and cation transport have been modelled and features in the vibrational spectra arising from the formation of local salt-polymer complexes have been explained. The internal flexibility, stable structures and the vibrational spectra of the often used TFSI anion, [(CF3SO2)2N-], and the corresponding acid HTFSI have been investigated.