EFFECT OF ELECTROLYTE-COMPOSITION ON THE PERFORMANCE OF SODIUM POLYMER CELLS/

The dependence on Na/P(EO)(n)NaX/NaxMnO2 (P(EO)=poly(ethylene oxide), X=CF3SO3 or (CF3SO2)(2)N)) cell cycle life and rate capability on poly mer electrolyte composition is described. Transition time experiments and mathematical modeling indicate that failure due to salt precipitat ion occurs at it(1/2)=10.5 to 21.4 mA s(0.5)/cm(2), when high initial concentrations of NaCF3SO3 are used in operating cells. Evidence for l arge ionic clusters in concentrated PEO/NaCF3SO3 solutions is also see n in the Raman spectroscopic data. Salt precipitation is a direct cons equence of the concentration gradients that arise during operation, du e to the negative cationic transference numbers (t(t)(0)) of the binar y saltipolymer electrolyte. By decreasing the initial salt concentrati on, t(+)(0) is increased, cell rate capability is doubled, and the cyc le life is enhanced nearly threefold. Similar improvements are obtaine d when PEO/NaN(CF3SO2)(2) electrolytes are used.