Synthesis and characterization of a new layered cathode material for sodium ion batteries

Owing to the high abundance of sodium and its low cost compared to lithium, sodium ion batteries have recently attracted a renewed interest as possible candidates for stationary and mobile energy storage devices. Herein, we present a new sodium ion intercalation material, NaxCo2/3Mn2/9Ni1/9O2, which has been synthesized by a sol–gel route in air followed by a heat treatment at 800 °C for 12 h. Its structure has been studied by X-ray diffraction showing that the material crystallized in a P2-type structure (space group P63/mmc). As far as the electrochemical properties of NaxCo2/3Mn2/9Ni1/9O2 as positive electrode are concerned, this compound offers a specific capacity of 110 mAh g−1 when cycled between 2.0 and 4.2 V vs. Na+/Na. The electrodes exhibited a good capacity retention and a coulombic efficiency exceeding 99.4%, as well as a reversible discharge capacity of 140 mAh g−1 when cycled between 2.0 and 4.5 V. These results represent a further step towards the realization of efficient sodium ion batteries, especially considering that the synthesis method proposed here is simple and cost effective and that all the electrochemical measurements were carried out without any use of additives or any optimization for both the materials and the cell components.