NiFe-NO3 Layered Double Hydroxide as a Novel Anode for Sodium Ion Batteries

2D materials are emerging materials for energy storage and among these layered double hydroxides (LDHs) seem particularly promising due to their structure, easily adjustable composition, and cheapness. This study marks the first reported application of an LDH, specifically NiFe-NO3 LDH, as conversion anode material in a sodium half-cell, to the best of our knowledge. Despite an initial loss in capacity, the material demonstrates notable stability, retains a high specific capacity even after 50 discharge/charge cycles (~ 500 mAh/g). The intricate reaction mechanism was explored using various ex-situ techniques such as DC magnetometry and FTIR, as well as in-operando X-ray Absorption Spectroscopy (XAS). The proposed Na-storage mechanism in NiFe-NO3 LDH involves an initial irreversible "activation" during the first sodiation, characterized by a phase change reaction that leads to the formation of NiOx and Fe3O4, followed by a reversible mechanism involving both intercalation and conversion in subsequent cycles.