Ultrahigh Phosphorus Doping of Carbon for High‐Rate Sodium Ion Batteries Anode

Abstract Phosphorus doped carbons are of particular interest as anode materials because of their large interlayer spacing and strong adsorption of Na⁺ ions. However, it remains challenging to achieve high phosphorus doping due to the limited choices of phosphorus sources and the difficulty in constructing oxygen‐free synthesis system. Herein, a new synthesis strategy is proposed to prepare ultrahigh phosphorus‐doped carbon (UPC) anodes for high performance sodium ion batteries (SIBs). By using two commonly available, miscible, evaporable liquids in PCl₃ and C₆H₁₂, as phosphorus and carbon sources, an oxygen‐free reaction system is successfully established by N₂ bubbling to simultaneously realize carbonization and in situ P doping. The P content can reach 30 wt%, much higher than most reported P‐doping carbon‐based materials. Furthermore, the doped P is dominated by substitutional P(C₃) protrusions in the carbon lattice, which can significantly enlarge the interlayer spacing and enhance the adsorption energy of Na⁺. When serving as the SIBs anode, the UPC delivers an ultrahigh reversible capacity of 510.4 mAh g⁻¹ with a rational operating voltage of 0.54 V, and the best rate capability of 397.1 mAh g⁻¹ at 10 A g⁻¹. This new strategy will effectively promote the practical application of hard carbon.