Conduction properties of PVDF-type polymer electrolytes with lithium salts, LiN(CF3SO2)(2) and LiN(C2F5SO2)(2)

Diffusion coefficients of gel electrolytes composed of lithium salts, LIN(C F,SO,), (Imide) and LiN(C2F5SO2)(2) (BETI), mixed solvent EC/DEC and copoly mer PVDF-HFP have been measured using the pulsed-field gradient NMR in orde r to investigate the conduction mechanisms of the gel electrolytes. The dif fusion values depended on the polymer to solution ratio of the gel. However , they were independent of the diffusion time in the range between 20 and 5 00 ms. This suggests there is no macroscopic blocking effect of the polymer as steric hindrance on the mobility in the migration range between 0.5 and 5 mum. The cation and anion diffusion values approximated each other with the increase in polymer fraction. Estimation of the relative change in carr ier concentration using the diffusion and conductivity values confirmed tha t the dissociation degree of the Imide gels changed orderly depending on th e polymer content, which may be due to some interaction between the mobile species and the polymer. (C) 2000 Elsevier Science B.V. All rights reserved .