New single ion conductors (“polyBOP” and analogs) for rechargeable lithium batteries

Phosphorus-containing single ion conducting polyanionic electrolytes have been synthesized from PCl5, oxalic acid (or catechol) and polyethylene glycols (or polypropylene glycols), using a stepwise procedure. The highest ambient conductivity of 10−5.8 S cm−1 is obtained for the polymer synthesized from oxalic acid and PEG600 (LiBOPEG600). While the ionic conductivity of the polymer formed from chloro bis(oxalato)borate (BOP) and PEG400 is nearly one order of magnitude higher than that of the polymer formed from BOP and PPG425, the ionic conductivity of the polymer formed from oxalic acid, PCl5 and PEG600 is only slightly higher than that of the polymer formed from catechol, PCl5 and PEG600. All the temperature dependence of the ionic conductivities shows curved Arrhenius plots, suggesting that the ion transport is closely associated with segmental motion of the polymer chain. Both the free-volume theory based William–Landel–Ferry (WLF) equation and the well-known Vogel–Tammann–Fulcher (VTF) equation are found to be valid for describing the conductivity data within the temperature range investigated.