Polymer electrolytes based on cross-linked cyclotriphosphazenes

Substituted cyclotriphosphazenes were used to prepare lithium ion conducting polymer networks. Two types of compounds were synthesized starting with the precursor hexachlorocyclotriphosphazene (HCCP): Type I (CVEEP) in which all the chlorine atoms in HCCP were replaced by vinyloxyethoxyethoxy groups (VEE = –OCH2CH2OCH2CH2OCHCH2), and type II (CVMEEP) in which half of the chlorine was replaced by VEE and the other half by methoxyethoxyethoxy groups (MEE = –OCH2CH2OCH2CH2OCH3). The terminal vinyl groups were used to build up a network by a thermally initiated cross-linking of lithium salt containing membranes. Polymer electrolytes with dissolved LiSO3CF3 and LiN(SO2CF3)2 were investigated by impedance measurements. The ionic conductivity of CVMEEP with 10 wt.% LiSO3CF3 was 3.2 × 10− 5 S/cm at 30 °C and 4.1 × 10− 4 S/cm at 90 °C. Lower conductivity values in the range 10− 8–10− 9 S/cm were obtained at 30 °C for the highly crosslinked CVEEP. An interesting polymer electrolyte with good mechanical properties and a good conductivity of 1.3 × 10− 5 S/cm (30 °C) was obtained from a solution of MEEP (= poly[bis(methoxy–ethoxy–ethoxy)phosphazene]) and LiSO3CF3 in CVEEP as an interpenetrating network.