Okra‐Like Fe<sub>7</sub>S<sub>8</sub>/C@ZnS/N‐C@C with Core–Double‐Shelled Structures as Robust and High‐Rate Sodium Anode
Dongwei Cao, Wenpei Kang, Wenhong Wang, Kaian Sun, Yuyu Wang, Ping Ma, Daofeng Sun
Abstract
Abstract Core–multishelled structures with controlled chemical composition have attracted great interest due to their fascinating electrochemical performance. Herein, a metal–organic framework (MOF)‐on‐MOF self‐templated strategy is used to fabricate okra‐like bimetal sulfide (Fe 7 S 8 /C@ZnS/N‐C@C) with core–double‐shelled structure, in which Fe 7 S 8 /C is distributed in the cores, and ZnS is embedded in one of the layers. The MOF‐on‐MOF precursor with an MIL‐53 core, a ZIF‐8 shell, and a resorcinol–formaldehyde (RF) layer (MIL‐53@ZIF‐8@RF) is prepared through a layer‐by‐layer assembly method. After calcination with sulfur powder, the resultant structure has a hierarchical carbon matrix, abundant internal interface, and tiered active material distribution. It provides fast sodium‐ion reaction kinetics, a superior pseudocapacitance contribution, good resistance of volume changes, and stepwise sodiation/desodiation reaction mechanism. As an anode material for sodium‐ion batteries, the electrochemical performance of Fe 7 S 8 /C@ZnS/N‐C@C is superior to that of Fe 7 S 8 /C@ZnS/N‐C, Fe 7 S 8 /C, or ZnS/N‐C. It delivers a high and stable capacity of 364.7 mAh g −1 at current density of 5.0 A g −1 with 10 000 cycles, and registers only 0.00135% capacity decay per cycle. This MOF‐on‐MOF self‐templated strategy may provide a method to construct core–multishelled structures with controlled component distributions for the energy conversion and storage.