Biomass-Derived Phosphorus-Doped Porous Hard Carbon Anode for Stable and High-Rate Sodium Ion Batteries

Biomass-derived hard carbon, despite being promising for anode material of sodium-ion batteries, usually suffer from low initial coulombic efficiency (ICE), poor rate capacity, and limited cycling stability caused by complex surface defects and low intrinsic conductivity. Herein, phosphorus-doped porous hard carbon (HC@PC-P) were synthesized by the thermal polymerization of soy lecithin on the surfaces of hard carbon derived from olive kernels. The incorporation of heteroatom phosphorus in the porous hard carbon framework expands the carbon lattice spacing, optimizes the graphitization degree, and increases electrical conductivity, guaranteeing ensuring rapid electron and ion transfer. These coupling effects enable HC@PC-P anode to achieve a high reversible capacity of 350 mAh g-1 at 0.1 A g-1, an impressive initial coulombic efficiency of 89.6 %, and remarkable long-term cycling stability at 1 A g-1 over 1000 cycles with negligible capacity fade. The mechanisms behind sodium storage and enhanced electrochemical performance were elucidated by ex-situ Raman spectroscopy and kinetic analysis. Additionally, the assembled HC@PC-P//Na3V2(PO4)3 full cell demonstrated a high energy density of 257.9 Wh kg-1. This work provides a rational guide for designing advanced hard carbon anode materials for high-energy sodium-ion batteries.