Polyphosphazene Electrolytes for Lithium Batteries

Poly([2-(2-methoxyethoxy)ethoxy]phosphazene), MEEP, doped with lithium salts, is a useful electrolyte for a "solid-state" lithium battery. We report characterization of MEEP by conductivity measurements, NMR and FTIR spectroscopy techniques, and observations of electrochemical activity related to lithium batteries. The P-31, C-13, and H-1 NMR spectra show characteristic peaks related to polyphosphazene with etheric side chain with minor cross-linking. FTIR spectra show that lithium is weakly associated with ethoxide groups of the polymer and resides in an energy well similar to 0.045 eV deep. The conductivity of undoped MEEP was found to be (2.5-5.0) x 10(-7) Omega(-1) cm(-1) and of doped MEEP, at the level of 0.17 mol of LiCF3SO3 per mole of monomer equivalent, to be similar to 2.5 X 10(-5), at ambient temperature. Cyclic voltammetry shows inefficiencies in the lithium redox reaction. The operation of Li/MEEP(LiClO4)/TiS2 cell at 30 mu A/cm(2) charge and 50 mu A/cm(2) on discharge indicates polarization during deintercalation of lithium from TiS2.