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

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.