Ionic conduction properties of PVDF-HFP type gel polymer electrolytes with lithium imide salts

Conduction properties of gel polymer electrolytes composed of lithium imide salts, LiN(CF3SO2)(2), LiN(C2F5SO2)(2), and PVDF-HFP copolymer were investigated using the pulsed-field gradient NMR and complex impedance techniques. The diffusion coefficients of the gel decreased with an increase in the polymer fraction in the gel. Carrier concentration exhibited 3 orders of magnitude variation in the fraction change in polymer from 80% to 20%. These results suggest that the polymer interacts with the electrolyte to affect the carrier concentration and mobility of the gel electrolytes. The interactive effect of polymer would be detected in the measurements of spin-lattice relaxation time (T-1). The deviation of the symmetric curve of the temperature dependence of T-1 could be divided into two components, one was consistent with the component of solution and independent of the polymer fraction and the other depended on the polymer fraction in the gel.