Metal Coordination Complex Derived Fe 7 S 8 Particles Embedded in N-doped Carbon Framework with Regulated Porous Structure Enabling High-Rate and Durable Sodium Storage.

Iron sulfides with high theoretical capacity confront the challenges of low rate capability and severe capacity fading for sodium storage, which are mainly caused by poor electron/ion transport kinetics and drastic volume fluctuations during cycling. Herein, to mitigate these obstacles, a multi-step synthetic tactic involving solvothermal, carbonization, and subsequent sulfurization is put forward for the construction of wire-like structure by confining Fe 7 S 8 particles in porous N-doped carbon framework (denoted as Fe 7 S 8 /PNC) using zinc iron nitrilotriacetate as template. By partially substituting Fe 3+ with Zn 2+ in the metal coordination complex, the porous structure of coordination complex derived carbon framework can be regulated through pore structure engineering of Zn nanodroplets. The desired porous and robust core/shell structure can not only afford favorable electron/Na +  transport paths and additional active sites for Na + storage, but also provide reinforced structural integrity of interior Fe 7 S 8  particles by retarding the pulverization and buffering the mechanical stress against volume fluctuations. As anode for sodium-ion batteries, the optimal Fe 7 S 8 /PNC delivers a high reversible capacity (743 mAh g -1  at 0.1 A g -1 ), superior rate capability (553 mAh g -1  at 10 A g -1 ), and long-term cycling stability (602 mAh g -1 at 5 A g -1 with 98.5% retention after 1000 cycles).