Regulate Phosphorus Configuration in High P-Doped Hard Carbon as a Superanode for Sodium Storage

Heteroatom-doped hard carbon is a popular method to optimize the electrochemical performance of anode electrodes for sodium-ion batteries. Herein, phosphorus-doped hollow carbon nanorods (P-HCNs) are obtained by a one-step synthesis with a high phosphorus content of 7.5 atom %. By controlling the P configuration, the P-HCNs03 exhibits reversible capacity as high as 260 mA h g^-1 at the current density of 1.0 A g^-1 after 500 cycles with an initial Coulombic efficiency (ICE) of 73%. When the amount of phosphorus in the as-prepared materials is changed, the different structures of the P-doped carbon lattices are analyzed by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Based on the first-principles calculation, although the P-O bond has the most configurations, the excellent reversible capacity of the electrode is attributed to the strong Na-absorption ability of P═O and P-C bonds. The sodium-based dual-ion batteries (NDIBs) assembled with P-HCNs03 as an anode and expanded graphite as a cathode (P-HCNs03//EG) exhibited a high energy density of 138 W h kg^-1 at a power density of 159 W kg^-1. The results provide an important angle to optimize the performance of hard carbons with other functionalized heteroatoms.