Regulating the breathing of mesoporous Fe0.95S1.05 nanorods for fast and durable sodium storage

Long-term cycling stability and high-rate capability have been the major challenges of sodium-ion batteries (SIBs) due to the uncontrollable electrode breathing including huge volume swelling/shrinking and serious ionic/electronic disconnection. Herein an efficient anode material consisting of mesoporous iron-sulfide (Fe0.95S1.05) combined with carbon/graphene double encapsulation (Fe0.95S1.05@C-rGO) is developed to effectively regulate the electrode breathing and realize durable and fast sodium storage. The mesoporous structure combined with double-carbon protection provides complete ionic/electronic circuits and robust structures that enable fast and durable electron/Na+ access to each of Fe0.95S1.05 nanocrystal. In situ transmission electron microscopy measurement reveals the structural evolution with reversible mesopores disappearance/recovery and small volume swelling/shrinking upon the sodiation/desodiation. As a consequence, the Fe0.95S1.05@C-rGO electrode delivers a high specific capacity (567.6 mAh g-1 at 100 ​mA ​g-1), excellent rate performance (323.5 mAh g-1 at 5000 ​mA ​g-1) and ultralong cycle life (more than 1700 cycles with 0.015% capacity decay per cycle). In situ X-ray diffraction and selected area electron diffraction patterns unveil that the Fe0.95S1.05@C-rGO electrode is based on a reversible conversion reaction. Moreover, a Fe0.95S1.05@C-rGO||Na3V2(PO4)3/C full battery is demonstrated, which delivers stable cycling (482.8 mAh g-1 at 500 mAh g-1) and excellent rate capability (445.9 mAh g-1 at 5000 ​mA ​g-1).