High-Entropy Materials as a Design Paradigm for Low-Temperature Sodium-Ion Batteries

Low-temperature (LT) operation remains a major barrier to the practical deployment of sodium-ion batteries (SIBs) because reduced thermal activation magnifies coupled limitations in bulk Na⁺ transport, phase stability, and interfacial kinetics, resulting in strong polarization growth, rapid capacity loss, and poor rate capability. Conventional optimization approaches based on incremental compositional tuning target a single bottleneck at a time and therefore struggle under sub-zero conditions, where transport and interphase evolution become tightly intertwined. High-entropy materials (HEMs) offer a distinct design paradigm in which configurational disorder is used as a controllable variable to reshape thermodynamics and kinetics, stabilize vulnerable frameworks, and broaden the distribution of accessible Na⁺ migration pathways. In this review, we analyze how entropy engineering influences LT performance across cathodes, anodes, electrolytes, and interfaces, emphasizing mechanistic links between realized disorder, transport activation penalties, and the accumulation of interfacial resistance in the solid-electrolyte interphase and cathode-electrolyte interphase. We synthesize quantitative descriptors and minimum reporting metrics that enable meaningful comparison across studies, and we highlight a unifying entropy-percolation framework connecting bulk ionic conduction with solvation/desolvation and interphase transport in liquid systems. We conclude by outlining key trade-offs, manufacturability constraints, and research directions required to translate high-entropy strategies into robust LT-SIB operation.