Sodium Solid‐State Electrolytes for Superior Ionic Conductivity

Composite solid electrolytes are central to the advancement of sodium‐based energy storage technologies, yet challenges in interfacial contact and mechanical reliability persist. In this study, NASICON‐containing polyethylene oxide (PEO)‐based composite electrolytes were fabricated with varying EO:Na ratios and NASICON contents. The optimized composition, with an EO:Na ratio of 15:1 and 25 wt% NASICON, achieved an ionic conductivity of 5 10 S cm at 30°C. A custom‐designed compression and temperature‐controlled test rig was developed specifically for this study to evaluate the mechanical response of the electrolyte under repeated compressive loading. Ionic conductivity measurements under low pressure (60 kPa) revealed a baseline value of 5.74 10 S cm. After two compressive cycles at 825 kPa, the conductivity increased to 6.81 10 S cm at room temperature, corresponding to an 18.6% enhancement due to improved interfacial contact. However, a third compression cycle induced interfacial deterioration and mechanical damage, resulting in conductivity loss. This structural degradation—manifested by local delamination and tearing—was confirmed through scanning electron microscopy (SEM) imaging. These findings demonstrate that controlled mechanical conditioning enhances transport properties up to a critical threshold, beyond which irreversible damage limits performance. The methodology presented offers insights into mechanical–electrochemical coupling in composite solid electrolyte systems.