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(CF3SO2)2 (Imide) and LiN(C2F5SO2)2 (BETI), mixed solvent EC/DEC and copolymer PVDF-HFP have been measured using the pulsed-field gradient NMR in order to investigate the conduction mechanisms of the gel electrolytes. The diffusion 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 500 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 μm. The cation and anion diffusion values approximated each other with the increase in polymer fraction. Estimation of the relative change in carrier concentration using the diffusion and conductivity values confirmed that the dissociation degree of the Imide gels changed orderly depending on the polymer content, which may be due to some interaction between the mobile species and the polymer.