Constructing stress-release layer on Fe7Se8-based composite for highly stable sodium-storage

Engineering multicomponent composite materials into tailored structure is of vital importance for developing advanced sodium ion batteries (SIBs). However, the mechanical stress intensification originating from severe volume expansion upon sodiation induces anisotropic swelling and anomalous structural changes, thus leading to electrode instability and inferior sodium storage performance. Herein, we propose a novel stress-release strategy by inserting of MoSe2 nanosheets onto the surface of yolk-shell Fe7Se8@C composite to accommodate the volume expansion and stabilize the electrode. Bestowed by the unique superiority, the Fe7Se8@C@MoSe2 composite manifests impressive sodium-storage performance in terms of high specific capacity (473.3 mAh g(-1) at 0.1 A g(-1)), excellent rate capability (274.5 mAh g(-1) at 5.0 A g(-1)) and long-term cycling stability (87.1% capacity retention after 600 cycles at 1.0 A g(-1)). Finite element (FE) simulations confirm that the exterior MoSe2 layer could significantly dissipate the stress caused by the sodiation-induced expansion of Fe7Se8 in the carbon layer. The primary sodium storage mechanisms and structural evolution are further revealed in details by in situ and ex situ investigations. More encouragingly, a practical sodium-ion full cell based on Fe7Se8@C@MoSe2 anode is demonstrated with remarkable performances. This work strengthens the fundamental understanding of mechanical effect for sodium-storage behaviors and sheds light onto designing smart multi-compositional hybrids toward advanced energy storage devices.