Realizing Fast Charge Diffusion in Oriented Iron Carbodiimide Structure for High-Rate Sodium-Ion Storage Performance.

Abstract

Iron carbodiimide (FeNCN) belongs to a type of metal compounds with a more covalent bonding structure compared to common transition metal oxides. It could provide possibilities for various structural designs with improved charge-transfer kinetics in battery systems. Moreover, these possibilities are still highly expected for promoting enhancement in rate performance of sodium (Na)-ion battery. Herein, oriented FeNCN crystallites were grown on the carbon-based substrate with exposed {010} faces along the [001] direction (O-FeNCN/S). It provides a high Na-ion storage capacity with excellent rate capability (680 mAh g^-1 at 0.2 A g^-1 and 360 mAh g^-1 at 20 A g^-1), presenting rapid charge-transfer kinetics with high contribution of pseudocapacitance during a typical conversion reaction. This high rate performance is attributed to the oriented morphology of FeNCN crystallites. Its orientation along [001] maintains preferred Na-ion diffusion along the two directions in the entire morphology of O-FeNCN/S, supporting fast Na-ion storage kinetics during the charge/discharge process. This study could provide ideas toward the understanding of the rational structural design of metal carbodiimides for attaining high electrochemical performance in future.