Composite single ion solid-state polymer electrolytes were prepared by blending lithiated
poly(perfluoroalkylsulfonyl)imide (PFSILi) ionene with poly(ethylene oxide) (PEO) at various PFSILi
contents. Their electrochemical performance was characterized by ionic conductivity, lithium ion
transport number, cyclic voltammetry and galvanostatic cycling in batteries. The composite PEO–PFSI-
25, containing 24.5% of PFSI, was found to have a maximum ionic conductivity of 1.76 104 S cm1 at
80 C. Because of the immobilization of the anionic perfluorosulfonimide groups on the backbone of
the ionene polymer with flexible and stable perfluoroether connectors, the composite had unusually
high electrochemical stability (up to 5.5 V vs. Li+/Li) and a low anion transference number. The PFSILi
unit interacts strongly with the PEO segments, resulting in the depression of PEO crystallization and the
formation of multi-dimensional ionic crosslinks within the composite to impart dimensional and cycling
stability to the electrolyte system. LiFePO4/Li battery prototypes using PEO–PFSILi polymer electrolytes,
with reversible capacity of 140 mA h g1 at 80 C and 0.2 C, were able to maintain 50 stable cycles for
1000 h at 70 C and 0.1 C.