Relationship between Intrinsic Properties and Homogeneity of Ionic Conductivity of CMCh/Paracrystalline ZSM-5 Zeolite/LiClO4 Composite Solid Electrolyte Membranes

Abstract

Evaluating the intrinsic properties of various compositions of composite solid electrolyte (CSE) membranes to determine their suitability for further development in electrochemical cells is a challenging process. In this study, the inherent characteristics of CSE membranes related to the homogeneity of their ionic conductivity were assessed by using Nyquist plots and the relative standard deviation (RSD) of ionic conductivity measurements. Among six combinations of carboxymethyl chitosan (CMCh, C), paracrystalline ZSM-5 zeolite (Z5AH, Z), and LiClO4 (L), the two membranes CZL10 (10 wt % LiClO4) and CZL25 (25 wt % LiClO4) displayed similar Nyquist plots across three regions of each membrane. These two samples also exhibited relatively low RSD values of ionic conductivity, 31.06% and 40.48%, respectively. The relatively low conductivity RSD reflects the membrane homogeneity. The uniformity of ionic conductivity of the CZL10 membrane with the lowest RSD value was further confirmed by the surface homogeneity observed through AFM analysis. Continuous incorporation of CMCh–Z5AH in the CZL10 membrane contributes to the surface uniformity. Meanwhile, the DSC data and water contact angle of CZL25 supported its conductivity uniformity. The uniformity of the surface arises from consistently spaced misfit dislocations. The approach offers a simple, cost-effective, and efficient method to identify suitable CSE compositions for further evaluation in battery and fuel cell applications.