Abstract
Sodium-ion batteries (SIBs) are potential candidates for next-generation grid-scale energy storage owing to their safety as well as the abundance of sodium resources. Further progress in SIB technology demands the advancement of cathode materials with outstanding performance. Among various cathode materials, layered transition metal oxides based on Ni, Fe, and Mn (NaNFM) have recently received great attention by combining the positive features of each of them. This review focuses on the most current developments in the study and design of NaNFM (Na x Ni y Fe z Mn 1−( y + z ) O 2 ) as a cathode material for SIBs, including synthesis methods, crystal structure/structural evolution during charge–discharging, and the effect of different molar ratios. Adjusting the transition elements enables formation in several phases that promote Na-ion diffusion, resulting in high-rate capability and cycle stability. Moreover, key strategies to improve the electrochemical performance through doping and surface modifications are discussed. Future optimization of these materials shows potential for enormous opportunities for implementing cost-effective and high-performance energy -storage technologies.