High‐Performance Flexible Freestanding Anode with Hierarchical 3D Carbon‐Networks/Fe7S8/Graphene for Applicable Sodium‐Ion Batteries

Abstract Sodium‐ion batteries (SIBs) have gained tremendous interest for grid scale energy storage system and power energy batteries. However, the current researches of anode for SIBs still face the critical issues of low areal capacity, limited cycle life, and low initial coulombic efficiency for practical application perspective. To solve this issue, a kind of hierarchical 3D carbon‐networks/Fe 7 S 8 /graphene (CFG) is designed and synthesized as freestanding anode, which is constructed with Fe 7 S 8 microparticles well‐welded on 3D‐crosslinked carbon‐networks and embedded in highly conductive graphene film, via a facile and scalable synthetic method. The as‐prepared freestanding electrode CFG represents high areal capacity (2.12 mAh cm −2 at 0.25 mA cm −2 ) and excellent cycle stability of 5000 cycles (0.0095% capacity decay per cycle). The assembled all‐flexible sodium‐ion battery delivers remarkable performance (high areal capacity of 1.42 mAh cm −2 at 0.3 mA cm −2 and superior energy density of 144 Wh kg −1 ), which are very close to the requirement of practical application. This work not only enlightens the material design and electrode engineering, but also provides a new kind of freestanding high energy density anode with great potential application prospective for SIBs.