Dynamic Sodiation-Driven Pore Reconstruction for Superior Initial-Coulombic-Efficiency and High-Rate in Xylose-Based Hard Carbon Anode

Abstract

The trade-off between initial coulombic efficiency (ICE) and rate performance of hard carbon anodes remains a challenge in their practical applications, which is highly related to their complex active surface and porous properties. In this work, a high-performance hard carbon anode is prepared using xylose as the carbon source with Co²⁺-assisted catalysis, which exhibits an excellent initial coulombic efficiency of 91.6%, a high capacity of 396.4 mA h g⁻¹, superior rate performance (176.3 mA h g⁻¹ at 5 A g⁻¹), and outstanding cycling stability. Cobalt-ion treatment forms “expanded” graphite segments, facilitating the intercalation of desolvated sodium ions. Additionally, the intersection of these graphite segments creates “nanocaves”, enabling rapid sodium-ion transport at the initial cycling stage. Using a combination of atomic-resolution structural characterization and three-dimensional electron tomography via transmission electron microscopy, it is observed that initially isolated nanoporous holes collapsed into interconnected pancake-like pores during later cycling. The reconstructed narrow but connected pore structure provides abundant sodium storage sites and rapid charge transfer pathways, effectively accommodating structural stress during cycling. This work presents an innovative strategy for designing commercial hard carbon anode with advanced pore architectures and also provides new insight into the structural evolution of hard carbon during cycling.