From Structure to Performance: Exploring MOF-Based Electrolytes for Enhanced Sodium-Ion Battery Conductivity.

Abstract

Energy storage systems (ESSs) are recognized as vital for sustaining industrial growth and the rising demand for portable and large-scale applications. Sodium-ion batteries (SIBs), using abundant sodium, offer an alternative to costly lithium-ion batteries (LIBs) but face challenges with lower energy density, slow ion transport, and limited cycle stability. This review critically examines metal-organic frameworks (MOFs) as next-generation electrolytes capable of addressing these challenges by following these mechanisms. High porosity and ordered channels (6-12 Å) facilitate uniform Na+ diffusion and reduce activation barriers from 1.23 to 0.36 eV, directly improving power density. Tunable functional groups with strategic electronegativity enable selective ion transport and dendrite suppression, thereby enhancing cycle stability. Framework versatility allows integration with polymers and ionic liquids, yielding ionic conductivities above 10-4 S cm-1 and boosting energy density. Charge transport occurs via both through-bond and through-space pathways, with the latter achieving up to 43-fold improvements in diffusion coefficients. By consolidating these findings, the review establishes a systematic structure performance framework: pore geometry governs ionic conductivity, functional groups control ion selectivity, and framework flexibility dictates mechanical stability during cycling. This MOF electrolytes development from empirical exploration to rational design, providing guiding principles and future directions for scalable, safe, and high-performance SIBs.