Insight on the Enhanced Reversibility of a Multimetal Layered Oxide for Sodium-Ion Battery

Sodium-ion layered cathodes range along a vast variety of structures and chemical compositions that influence the physical-chemical characteristics and the electrochemical features in battery. In this work, we show that the synergistic effects of various metals, enhanced structure, and optimal morphology of Na0.48Al0.03Co0.18Ni0.18Mn0.47O2 material lead to remarkable reversibility in a sodium cell. X-ray diffraction refinement evidences that the electrode has a P3/P2-type layered structure, whereas scanning electron microscopy study shows a morphology consisting of primary layers with nanometric thickness regularly stacked into uniform micrometric particles. In-depth investigation combining ex situ X-ray diffraction, galvanostatic intermittent titration, and voltammetry measurements reveals solid-solution Na+ intercalation into the layered oxide between 1.4 and 4.6 V versus Na+/Na with relevant lattice stability. Furthermore, the study shows the absence of phase transitions during Na+ exchange within the material framework, which advantageously leads to enhanced reversibility, benefiting from minor lattice change upon Na+ intercalation, fast diffusion, improved electrode/electrolyte interphase, and smooth voltage profile. Hence, the electrode delivers a maximum capacity of about 175 mAh g-1 with suitable cycling stability and a Coulombic efficiency approaching 99% in a sodium cell. Therefore, we believe that the study reported herein may shed light on important characteristics of this attractive class of electrodes, allowing efficient operation in next-generation sodium-ion batteries.