Nano-Restricted Structures in Hard Carbon Anodes: Mechanisms and Optimization

Nano-restricted structures (NRS) refer to spatially restricted domains or channels constructed at the nanoscale through physical or chemical methods, whose unique confinement effects profoundly regulate the transport, storage, and reaction behaviors of substances. As a critical structural component in hard carbon (HC) anode materials, the precise design and regulation of NRS play a decisive role in enhancing the comprehensive performance of HC. However, the underlying sodium storage kinetics and multiscale synergistic mechanisms within these NRS remain insufficiently understood. This paper systematically reviews the controllable synthesis strategies, formation mechanisms, structure-property relationships, advanced characterization techniques, and performance optimization approaches for NRS in HC anodes, elucidating the physicochemical essence and multidimensional synergistic mechanisms behind their performance enhancement. Furthermore, the key insights proposed herein provide critical theoretical guidance and technical support for the rational design of high-performance HC anode materials and their practical implementation in sodium-ion batteries.