Bicontinuous Structure Mediated Microstructural Engineering of Hard Carbon for Enhanced Sodium Storage

Abstract Sodium‐ion batteries (SIBs) are a promising energy storage technology due to the abundance and low cost of sodium resources. However, their practical application is hindered by challenges, including high irreversible capacity loss during initial cycles, poor rate performance, and structural instability. Here, a bicontinuous mesoporous hard carbon with a single primitive (SP) microstructure (coined SP–HC) is introduced that addresses these limitations through microstructural engineering. This SP–HC design increases the density and accessibility of Na + storage sites, enhances carbon disorder, and expands interlayer spacing, leading to improved sodium storage capacity and kinetics. The 3D continuous meso‐channels enable rapid Na + transport, achieving an exceptional rate performance of 172 mAh g −1 at 10 A g −1 (full charge in 1 min). Remarkably, the SP–HC anode exhibits unprecedented cycle stability, retaining a high capacity of 80 mAh g −1 even after 100 000 cycles at a high current density of 10 A g −1 , which represents the best cycle stability reported for hard carbon‐based anodes of SIBs. This study provides an insight into the critical role of microstructural engineering in optimizing electrochemical storage of hard carbon anodes for SIBs.