Influence of crystallinity on ion conductivity of PEO-based solid electrolytes for lithium batteries

In this work, poly(vinyl chloride) (PVC)/poly(ethylene oxide) (PEO) polymer electrolytes for secondary batteries were prepared using a solution casting technique. In addition, their crystallinity, ionic conductivity and mechanical properties were investigated. A binary mixture of carbonate solvent was used as a plasticizer, and lithium perchlorate (LiClO₄) was used as a salt. The morphology and mechanical properties of the polymer electrolytes were characterized by scanning electron microscopy (SEM) and a universal tensile machine (UTM). The crystallinity of the polymer electrolytes was evaluated by differential scanning calorimetry (DSC). The ionic conductivity of the polymer electrolytes was measured using the frequency response analyzer (FRA) method. As a result, the mechanical properties of the polymer electrolytes did not show any significant changes up to 5 wt%, despite the phase separation of the composite. The ionic conductivity of polymer electrolytes containing 2 wt% PVC showed the highest ionic conductivity, 2.35×10^-3 (S/cm) at 25 °C. This ion conductivity was dependent on the reduced crystallinity by the addition of PVC moieties.