High Tap Density Co and Ni Containing P2‐Na0.66MnO2 Buckyballs: A Promising High Voltage Cathode for Stable Sodium‐Ion Batteries

Abstract Constructing high voltage (>4.5 V) cathode materials for sodium‐ion batteries has emerged in recent years to replace lithium batteries for large scale energy storage applications. Herein, an electrochemically stable Na 0.66 (Ni 0.13 Mn 0.54 Co 0.13 )O 2 (Na‐NMC) buckyballs with an uniform size of 5 µm and a high tap density of 2.34 g cm −3 , which exhibit excellent cyclability even at the high current with a cut‐off voltage of 4.7 V, is demonstrated. The Na‐NMC buckyballs are prepared from (Ni 0.13 Mn 0.54 Co 0.13 )CO 3 (NMC) precursor synthesized using a facile hydrothermal method. The Na‐NMC delivers a reversible capacity of around 120 mAh g −1 between 4.7 and 2 V at 1 C rate along with an excellent cyclic stability (90%) until 150 cycles, which is one of the best outcomes among the reported P2‐type cathodes tested at the high operating voltage range. Furthermore, Na‐NMC‐180 buckyballs with a high tap density is offering an enhanced volumetric energy density, a superior rate performance and an outstanding cyclic stability. The X‐ray adsorption fine structure analysis is used to study the local electronic structure changes around the Co, Mn, and Ni after cycling process at 1 C rate. The findings open opportunities for tailoring high‐performance and high‐energy cathode materials for sodium‐ion batteries.