Confining MOF-derived SnSe nanoplatelets in nitrogen-doped graphene cages via direct CVD for durable sodium ion storage

Tin-based compounds are deemed as suitable anode candidates affording promising sodium-ion storages for rechargeable batteries and hybrid capacitors. However, synergistically tailoring the electrical conductivity and structural stability of tin-based anodes to attain durable sodium-ion storages remains challenging to date for its practical applications. Herein, metal-organic framework (MOF) derived SnSe/C wrapped within nitrogen-doped graphene (NG@SnSe/C) is designed targeting durable sodium-ion storage. NG@SnSe/C possesses favorable electrical conductivity and structure stability due to the "inner" carbon framework from the MOF thermal treatment and "outer" graphitic cage from the direct chemical vapor deposition synthesis. Consequently, NG@SnSe/C electrode can obtain a high reversible capacity of 650 mAh·g^-1 at 0.05 A·g^-1, a favorable rate performance of 287.8 mAh·g^-1 at 5 A·g^-1 and a superior cycle stability with a negligible capacity decay of 0.016% per cycle over 3, 200 cycles at 0.4 A·g^-1. Theoretical calculations reveal that the nitrogen-doping in graphene can stabilize the NG@SnSe/C structure and improve the electrical conductivity. The reversible Na-ion storage mechanism of SnSe is further investigated by in-situ X-ray diffraction/ex-situ transmission electron microscopy. Furthermore, assembled sodium-ion hybrid capacitor full-cells comprising our NG@SnSe/C anode and an active carbon cathode harvest a high energy/power density of 115.5 Wh·kg^-1/5, 742 W·kg^-1, holding promise for next-generation energy storages.