Insight into ion dynamics in a NaClO4-doped polycaprolactone solid polymer electrolyte for solid state batteries

Abstract

Employing low T_g polymers has fundamental limitations in providing the desirable ionic conductivity at ambient temperature due to the freezing of chain dynamics. The stiffening of polymer chains and the formation of highly ordered systems due to the crosslinks have influenced the ionic conductivity. Ionic conductivity of 1.02 × 10⁻⁵ S cm⁻¹ was attained for the system that presented a quantum mechanical tunnelling mode of ion transport. A Na-ion transference number of 0.31 was achieved for 30 wt% of NaClO₄ salt in a polycaprolactone (PCL) matrix with an electrochemical stability window of 3.6 V at 25 °C. High crystallinity and limited availability of free Na⁺ ions in the electrolyte have resulted in lower ionic conductivity. PCL–NaClO₄ exhibited brilliant thermal stability and mechanical properties. The influence of cathode materials MnO₂, V₂O₅ and I₂ on the discharge characteristics of an electrochemical cell in the configuration cathode |(70 wt%)PCL–NaClO₄(30 wt%)|Na has been studied.