Synthesis and properties of Na_0.8Ni_0.4Mn_0.6O₂ oxide used as cathode material for sodium ion batteries

Abstract

A new P2-structured oxide Na_0.8Ni_0.4Mn_0.6O₂ was synthesized using a solid reaction method in which Na₂CO₃, MnO₂ and NiO were used as starting materials. This oxide has a high amount of electrochemically active Ni and exhibits good electrochemical intercalation behavior of Na ions, including good rate capability and good cycle performance at both room temperature and elevated temperature. It displays two apparent voltage plateaus at about 3.6 and 3.3 V, and its discharge capacity reaches 92 mAh·g⁻¹ at 0.1C in the voltage range of 2.0–4.0 V. At 1.0C, its discharge capacity reaches 85.3 mAh·g⁻¹. After 80 cycles at different current rates, the as-prepared sample exhibits good capacity retention. At elevated temperature of 55 °C, the discharge capacity remains the same at low current rate of 0.1C, but at high current rate of 1.0C, the discharge capacity is a little lower than that at room temperature.

Graphical Abstract

The first discharge capacity of the as-prepared Na/Na_0.8Ni_0.4Mn_0.6O₂ cell is about 158 mAh·g⁻¹ at 0.1 C rate in the voltage range of 2.0–4.5 V. In the subsequent charge–discharge process, its discharge capacities are about 92 mAh·g⁻¹ at 0.1C, 90 mAh·g⁻¹ at 0.2C, 87.9 mAh·g⁻¹ at 0.5C and 85.3 mAh·g⁻¹ at 1.0C.