Conduction mechanisms of PVDF-type gel polymer electrolytes of lithium prepared by a phase inversion process

Lithium gel electrolytes composed of the PVDF polymer produced by the phase inversion method and the EC/DEC solution of LiN(CF3SO2)(2) were prepared to investigate the conduction mechanisms in comparison with another type of gel from the conventional casting technique. The conductivity of the gel increased with the increase in the immersion time of the polymer membranes into the solution, indicating that it takes a certain time to form stable and homogeneous gels. The diffusion coefficients of the gel showed two diffusion components associated with the two different phases present before the equilibrium state. From these conduction properties as well as the morphological features speculated from the SEM photographs, we can say that there are two processes in the gel formation, introduction of the solution from the outside to the cavities of the host polymer and the subsequent penetration of the solution into the cavities in the polymer chains to form a swollen gel. Further, ionic conduction of the gel is dominated by the swollen gel in which the heterogeneous interaction between the polymer and the carriers or the salts before dissociation determines the mobility and content of the carrier. This result is consistent with the conduction properties confirmed for the gel prepared by the casting technique.