Sodium ion batteries (SIBs), as an alternative and promising energy storage system, have attracted considerable attention due to the abundant reserves and low cost of sodium. However, it remains a great challenge to achieve high capacity and rate capability required for practical applications. Herein, hollow octahedral Co3Se4 particles encapsulated in reduced graphene oxide (Co3Se4@rGO) were designed and synthesized and exhibited excellent electrochemical performances as anodes of SIBs, especially rate capability. Sodiation/desodiation processes and involved mechanisms were investigated by using in situ TEM and in situ XRD. During sodiation, a crystalline Na2Se layer with numerous amorphous fine Co nanoparticles dispersed on it was observed to appear on the surface of the original Co3Se4@rGO particles, and the movable Co-Na2Se composites further migrated to the rGO network with high electron/ion dual conductivity, resulting in ultrafast sodium storage kinetics and remarkable rate performance of the Co3Se4@rGO anode evidenced by delivering a discharge capacity of 229.3 mAh g-1 at a large current density of 50 A g-1. Our findings reveal the fundamental mechanism behind the enhanced performance of the Co3Se4@rGO anode and offer valuable insights into the rational design of electrode materials for high-performance SIBs.
Keywords: hollow octahedral Co3Se4@rGO; in situ TEM; in situ XRD; rate performance; sodium ion batteries.