Di-ureasil hybrids doped with LiBF4: Spectroscopic study of the ionic interactions and hydrogen bonding

In the present work Fourier transform infrared and Raman spectroscopy were used to characterize the cation/polymer, cation/cross-link, cation/anion and hydrogen bonding interactions in hybrid electrolytes composed of lithium tetrafluoroborate (LiBF4) and di-urea cross-linked poly(oxyethylene) (POE)/siloxane hybrid networks (di-ureasils) designated as d-U(2000) and d-U(600) and incorporating polyether chains with ca. 40.5 and 8.5 oxyethylene repeat units, respectively. Samples with a> n greater than or equal to 2.5 (where n, composition, is the molar ratio of CH2CH2O units per Li+ ion) were analyzed. In both di-ureasil systems over the whole range of salt content examined the Li+ ions bond to the ether oxygen atoms of amorphous POE chains and to BF4 - ions forming ion contact pairs. Spectroscopic evidences and SEM images confirm the presence of a crystalline POE/LiBF4 complex of unknown stoichiometry at n