Navigating ionic conductivity in MOF electrolytes: addressing measurement pitfalls and performance limits

Abstract

Solid-state batteries promise significant improvements in energy density and safety over conventional liquid-electrolyte systems, yet realizing their full potential hinges on developing solid electrolytes with high ionic conductivity and long-term cycling stability. Metal–organic frameworks (MOFs) have emerged as attractive candidates due to their high porosity, tunability, and structural versatility. However, integrating MOFs into solid-state batteries faces several critical challenges, such as high interfacial resistance, chemical reactivity at electrode–electrolyte interfaces, mechanical brittleness during cycling, and parasitic proton conduction. These issues are compounded by persistent pitfalls in accurately characterizing ionic conductivity, including ambiguities in distinguishing intrinsic Li⁺ transport from extrinsic protonic or solvent-mediated contributions and a lack of standardized measurement protocols. In this review, we first explore the interplay between MOF structural features and ion transport mechanisms. Then, we critically assess current strategies to overcome interfacial, chemical, and mechanical barriers, including composite membrane fabrication, defect engineering, and framework design. Finally, we propose best practices for electrochemical impedance spectroscopy (EIS) and cycling tests, emphasizing rigorous controls to decouple intrinsic ion conduction from extrinsic contributions. By addressing material and methodological challenges, this work aims to advance the development and accurate evaluation of MOF-based electrolytes for next-generation energy storage applications.