Evolution in electrochemical performance of the solid blend polymer electrolyte (PEO/PVDF) with the content of ZnO nanofiller

All-solid-state lithium-ion batteries are becoming more and more important due to their extremely high security and reliability. However, the electrochemical performance is unsatisfactory for the widely investigated solid polymer electrolytes (SPEs) based on polyethylene oxide (PEO) due to its high crystallinity. In order to solve the above shortcoming, the solid blend polymer electrolyte of PEO and polyvinylidene fluoride (PVDF) containing ZnO nanofiller with outstanding electrochemical performance was successfully prepared by an ameliorated method. The influences of ZnO nanofiller content on crystallinity, mechanical properties and electrochemical performance with respect to ion conductivity, lithium-ion migration number, cycle stability and rating capability of SPEs were systematically investigated. The results showed that the crystallinity of SPEs presented the first downward, and then upward tendency with the increase in content of ZnO nanofiller, resulting in the lowest crystallinity obtained in the SPE with 2 wt% ZnO (5.05%). The SPE with 2 wt% ZnO also demonstrated the optimal mechanical properties with the highest tensile/breaking strength (2.349/1.401 MPa) and elongation after breaking (241.911%). The similar tendency was also observed in electrochemical performance. The highest ion conductivity (3.145 × 10⁻⁴ S cm⁻¹ at 60 °C) and lithium-ion migration number (0.768 at 60 °C) were obtained on the SPE with 2 wt% ZnO. In addition, the coin cell containing the SPE with 2 wt% ZnO presented an excellent cycle stability (more than 1000 h) and rating capability (a high retention rate of 63.02% in discharge specific capacity with the current density increased from 0.1 C, 0.2 C, 0.5 C, 1 C, 2–3 C in turn, finally reduced to 1 C) at 60 °C, which were far higher than those of the SPE without ZnO. The research indicated that introducing the suitable content of ZnO nanofiller contributed to the improvement in electrochemical performance. On the contrary, the over addition of ZnO caused the reduction in electrochemical performance due to the agglomeration of ZnO nanofiller.