A comprehensive study of the role of transition metals in O3-type layered Na[NixCoyMnz]O2 (x = 1/3, 0.5, 0.6, and 0.8) cathodes for sodium-ion batteries

Abstract

A comprehensive study of Na[Ni_xCo_yMn_z]O₂ (x = 1/3, 0.5, 0.6, and 0.8) cathodes is carried out to determine the optimal composition as the electrochemical, structural, and thermal properties of O3-type layered cathodes are strongly dependent on the transition metal composition. Here, the role of each transition metal in [Ni_xCo_yMn_z]O₂ cathodes is identified via electrochemical property characterization, structural analysis, and thermal stability testing. Briefly, an increase of the Ni fraction resulted in an increasingly higher capacity but is accompanied by progressively poor capacity retention. On the other hand, the Co metal played an important role in stabilizing the structure, while the Mn content contributed to enhancing the capacity retention and thermal stability. The present study highlights the importance of appropriately balancing the transition metal composition in a layered Na[Ni_xCo_yMn_z]O₂ cathode. Furthermore, this work provides a design guideline for developing an ideal Na[Ni_xCo_yMn_z]O₂ cathode with both high capacity and optimal cycle retention in addition to thermal stability.