Solvent free PEO-NaClO4:Na3Zr2Si2PO12 composite solid polymer electrolytes: Comparison of conductive properties of “ceramics-in-polymer” and “polymer-in-ceramics”

In this work, a comparative study of the conductive properties of the PEO-NaClO4:NZSP composite solid polymer electrolyte (SPE) films was carried out in a wide range of the NZSP filler content (5–250 wt%), and the “ceramics-in-polymer” and “polymer-in-ceramics” fields were studied. The optimal composition of EO:NaClO4 with molar ratio is 10:1 to obtain SPE films with low crystallinity (12.2%) and high ionic conductivity (1.7∙10−5 S∙cm−1 at 30 °C) was determined. An additional reduction in crystallinity to 4.5% was achieved due to the introduction of NZSP filler. High ionic conductivity and low apparent activation energy were obtained with a content of NZSP filler of 25 wt% (σ = 3.56∙10−5 S∙cm−1 (30 °C) and Ea = 0.118 eV) for “ceramics-in-polymer” and 150 wt% (σ = 2.74∙10−5 S∙cm−1 (30 °C) and Ea = 0.116 eV) for “polymer-in-ceramics” fields. The Na+ ion transference number tNa+ was determined for PEO-NaClO4 and PEO-NaClO4:NZSP composites. The introduction of NZSP filler increases tNa+ from 0.45 (EO:NaClO4 = 10:1) to 0.55 (25 wt% of NZSP filler) and 0.77 (150 wt% of NZSP filler). The NVP||PEO-NaClO4:NZSP-150 wt%||Na half-cell was tested at 60 °C and the average charge-discharge capacity of ∼60 mAh·g−1 was achieved.