In Situ Reconstruction of Pseudographitic Carbon Microcrystallites With Rich Closed Nanopores for Extended Sodium Plateau Storage

ABSTRACT As anode materials, hard carbons hold promising applications for sodium ion batteries; however, the controllable tuning of carbon microstructure remains a critical challenge that slows down the industrialization pace. In this work, we propose an in situ reconstruction strategy to modulate the microstructure of bituminous coal‐derived hard carbon through a bifunctional molecule of phytic acid. The as‐formed P‐O‐C crosslinked network can serve as an in situ structure director, which offers steric hindrance to suppress carbon restacking and simultaneously chemical etching to create nanopores. Pseudographitic carbon microcrystallites with rich closed nanopores surrounded by thin, twisted, and interlayer‐expanded graphene sheets are delicately reconstructed for enhanced sodium storage. This microstructural virtue significantly enables extended sodium plateau capacity by 47.7%, resulting in a boosted reversible capacity of 372 mAh g −1 at 0.02 A g −1 with a high initial Coulombic efficiency of 87.2%. Fundamental insights into the charge storage mechanism and interface dynamics are unraveled by in/ex situ characterizations. This work offers an effective pore‐regulated method to design and fabricate advanced hard carbons for sodium‐ion batteries.