Low-crystallinity conductive multivalence iron sulfide-embedded S-doped anode and high-surface area O-doped cathode of 3D porous N-rich graphitic carbon frameworks for high-performance sodium-ion hybrid energy storages

Abstract

Sodium-ion hybrid energy storages (SIHESs) are promising electrochemical energy storages for many applications, but their low energy and power densities are yet to be overcome. Herein, we report a strategy to realize ultrahigh-energy density and fast-rechargeable SIHESs. Ultrafine iron sulfide-embedded S-doped carbon/graphene (FS/C/G) anode materials are synthesized from iron-based metal-organic framework (MOF)/graphene oxide heterostructures via graphitic carbon formation and sulfidation. Operando and ex-situ analyses reveal that cycled iron sulfides are rescaled into low-crystallinity conductive fragments with Fe vacancies and multivalence Fe2+/Fe3+ states. Size reduction to fragments inside a 3D porous S-doped N-rich graphitic carbon framework induces high-capacity/high-rate FS/C/G performance. Moreover, 3D porous O-doped carbon cathode materials are synthesized from zeolitic imidazolate frameworks (ZIFs) via pyrolysis-assisted micropore and KOH-assisted mesopore formations. This ZIF-derived porous carbon (ZDPC) has a ∼20-fold higher surface area (3972 m2/g) than conventional ZDCs, O-induced micropores/N-rich sites for high capacity, heteroatom-induced ion-accessible defects/mesopores, and N-rich conductive graphitic carbon networks. Additionally, FS/C/G//ZDPC SHHES benefits from diffusion-controlled and capacitive reactions, as demonstrated by its hitherto highest energy density of 247 Wh kg-1 outperforming state-of-the-art SIHESs, fast-rechargeable power density (up to 34,748 W kg-1) exceeding battery-type reactions by more than 100 folds, and cycle stability with ∼100 % Coulombic efficiency over 5000 charge-discharge cycles.