Structure of liquid PEO-LiTFSI electrolyte

The structure of a polymer electrolyte, P(EO)7.5LiN(SO 2CF (3))(2), has been determined by neutron diffraction with isotropic substitution. The Li ions are bonded on average to five ether oxygens belonging to pairs of PEO coils. These are arranged with a considerable degree of extended-range order providing pathways for the Li ion conduction. The lack of ion pairing in this system below 4.8 A is reminiscent of that observed in the remarkable structure of P(EO)6LiAsF (6) and implies that anions and cations are free to migrate independently.