Effect of the Morphological Features of the Poly(vinylidene difluoride)-Based Gel Electrolytes on the Ionic Mobility for Lithium Secondary Batteries

Highly conductive solid electrolytes used in energy storage systems could be developed by the systematic control of the ion conduction mechanism in the solid medium. In this study, we evaluated the ion migration mechanism of poly(vinylidene difluoride) (PVDF) gel electrolytes in relation to the structural/morphological features of the physically cross-linked PVDF gels. By measuring the spin–spin relaxation times ( T 2 ) of the cation/anion species of the quenched gel electrolytes, we found that anions with short T 2 were located close to the crystalline phase forming the cross-links, while cations with long T 2 were located in the solution-rich amorphous phase. The discrete locations of the cations and anions are suitable for preferential cation transport because the anions are restricted in the crystalline phase by the anion/crystallite interactions, as confirmed by the estimation of the microviscosity (β an ). Enhancing the cation mobility by controlling the two-phase condition of the PVDF gel is a new and promising approach for obtaining electrolytes that can be applied in high-power batteries.