Sodium-Ion Batteries: A Promising Alternative to Lithium-Ion

In recent years, sodium-ion batteries have emerged as an economical and sustainable alternative to lithium-ion batteries. Sodium, the sixth most abundant element on Earth, offers lower material costs and greater availability compared to lithium-ion batteries. The design of cathode materials plays a crucial role in the battery's lifespan and stability. Layered sodium manganese oxide (NaMnO2) has garnered increasing attention from researchers for its application as a cathode material in sodium-ion batteries. There are two crystal forms of NaMnO2: α-NaMnO2 and β-NaMnO2. The α-phase features a monoclinic layered structure, where planar MnO2 layers are composed of edge-sharing distorted MnO6 octahedra, alternating stacked with sodium ions at the center. In contrast, β-NaMnO2 has wavy or sawtooth edge-sharing distorted MnO6 octahedral layers, also interspersed with sodium ions. The synthesis of β-NaMnO2 typically requires higher temperatures, which often results in a sodium ion deficiency phase. To prevent the formation of sodium ion deficiency phases, efforts have been made to prepare non-equilibrium β phases that exhibit various defects, the most notable being stacking faults (SF), formed by the slip of crystal b-c planes, generating stacking fault sequences similar to the α phase.