Balancing Defects and Microcrystals in Carbon Anodes by Molecular Chemistry Method for Sodium-Ion Batteries

Carbon materials with large capacity and low potential serve as promising anode materials for sodium-ion batteries (SIBs). Carbon defects offer active sites for sodium storage but sacrifice reversibility, whereas carbon microcrystals improve conductivity but may suffer from low capacity. Herein, the balance between defects and microcrystals is realized by the molecular chemistry method of cross-linking and defect repairing. Real-time spectroscopic analyses reveal that the decomposition of tetrabromophthalic anhydride (TBPA) molecule induces the dehydrogenation of pitch to release small gas molecules to form pseudo-closed pores, followed by the cross-linking of C═O bonds in TBPA with the dehydrogenated pitch to form C─O─C bonds and thus suppress the excessive microcrystal growth. Meanwhile, the decomposition products of TBPA can also react with the dehydrogenated pitch to repair carbon defects. Thanks to the microstructure balance, the as-synthesized carbon material exhibits a smoother ion mass transfer channel (d₍₀₀₂₎ = 0.386 nm, La = 4.56 nm) and a larger storage space (V_{pseudo-closed pore} = 0.086 cm³ g^-1) than the pitch carbon (PC, d₍₀₀₂₎ = 0.349 nm, La = 5.90 nm, V_{pseudo-closed pore} = 0.041 cm³ g^-1), increasing the capacity from 162.5 to 336.5 mAh g^-1. This work sheds a chemical light on regulating carbon material microstructure for advanced SIBs.