LOCAL-STRUCTURE STUDIES OF PEO-BASED NIBR2 ELECTROLYTES

The local atomic arrangements surrounding Ni(II) and Br(-I) in a high molecular weight PEO (mol.wt = 5 x 10(6)) electrolyte of composition, NiBr2(PEO)8, were determined using K-edge EXAFS [Ni(II)] and AXS techniques [Br(-I)]. The results show that the first nearest neighbors of Ni(II) include, on average, four oxygens and two bromides, at distances from Ni(II) of 2.09 and 2.48 angstrom, respectively. Around Br(-I) are, on average, one Ni(II) ion and four carbons at distances of 2.48 and 2.58 angstrom, respectively. The two techniques yield consistent results and clearly show that ion pairing occurs in the electrolyte. The results indicate that Br(-I) ions are bonded more weakly in their local environments and thus likely to be more mobile than Ni(II) ions.