A facile strategy to prepare (N, Ni, P) tri-doped echinus-like porous carbon spheres as advanced anode for lithium ion batteries

Heteroatom doped carbon nanomaterials are often employed as advanced anodes for lithium ion batteries (LIBs) because of their stable structure, high capacity and low cost. In this work, we proposed a novel strategy to synthesize high density (N, Ni, P) tri-doped echinus-like porous carbon spheres (PCS) by carbonizing a metal-organophosphine framework (MOPF) directly. The MOPF employs riboflavin sodium phosphate (C₁₇H₂₀N₄NaO₉P) as an organic ligand as well as a nitrogen and phosphorus source to conjugate with Ni(NO₃)₂ • 6H₂O. As an anode for LIBs, PCS was demonstrated with discharge capacities that were able to reach 386.5 mAh • g^-1 after 100 cycles at a current density of 0.05 A • g^-1. Besides, the stable reversible capacities were obtained from ∼459 mAh • g^-1 to ∼91.8 mAh • g^-1 when the current density was varied from 0.05 to 1 A • g^-1. The good anode performance is attributed to the unique structure of PCS and (N, Ni, P) tri-doping which introduces the additional capacities due to the presence of the 'reservoir effect'. Moreover, the electrochemical analysis implied that the surface-limited capacitive behavior dominantly contributes to the lithium ion storage capacity of the PCS anode.