Manipulating Closed‐Pore Formation and Homogeneous SEI of Hard Carbon Anodes for Highly Reversible Sodium Storage

Abstract Despitelow cost and abundant sources, hard carbon (HC) anodes for sodium‐ion batteries (SIBs) exhibit a low initial Coulombic efficiency (ICE) owing to the unstable solid‐electrolyte interphase (SEI). In contrast, soft carbon (SC) anodes, demonstrating inferior sodium storage performance, possess a smoother surface facilitating the ordered growth of the SEI. To leverage the complementary advantages ofthem, a hard/soft carbon heterointerface material (x‐SMCC) is synthesized via a one‐step hydrothermal co‐assembly of microcrystalline cellulose and Perylene‐3,4,9,10‐tetracarboxylic dianhydride, following controlled carbonization. The integration of SC modifies the HC interface, reconstructing its surface structure, which significantly guides the formation of sodium clusters within the low‐potential plateau region. Moreover, the ordered SC phase serves as an effective substrate to guide the formation of a smoother SEI, thereby enhancing the overall electrochemical performance. Specifically, the optimized 5‐SMCC delivers an outstanding reversible capacity of 353.98 mAh g −1 at a current density of 30 mA g −1 , along with an enhanced ICE of 84.52%. Moreover, it retains 78% of its initial capacity after 1000 cycles at 1.5 A g −1 . This structural engineering strategy not only facilitates the development of cost‐effective HC anodes for practical SIBs but also offers a systematic design methodology for defect‐engineered carbonaceous anode materials.