文摘
On the basis of resource abundance and low cost, high capacity layered P2-type Na<sub>2/3sub>Fe<sub>1/2sub>Mn<sub>1/2sub>O<sub>2sub> material is regarded as a potential cathode material for sodium-ion batteries but suffers from its unstable structure during cycling. In this work, P2-type Na<sub>2/3sub>Fe<sub>1/2sub>Mn<sub>1/2sub>O<sub>2sub> layered materials were synthesized by a chelating agent assisted sol–gel method with NH<sub>3sub>·H<sub>2sub>O. With the addition of NH<sub>3sub>·H<sub>2sub>O and the control of the synthesis conditions, highly active material with a more stable structure and better electrochemical performance was obtained. Furthermore, the influences of structure changes during different voltage ranges (1.5–4.0 V and 1.5–4.3 V vs Na<sup>+sup>/Na) on the Na<sup>+sup> storage behaviors were also evaluated and compared. It is confirmed that, when being charged to 4.2 V, an OP4-type phase emerges, which can reduce the damage by the gilding of the MeO<sub>2sub> layers but leads to an unstable crystal structure. For long-term cycling, it is preferred to cut off at 4.0 V rather than at 4.3 V. For the optimized P2-type Na<sub>2/3sub>Fe<sub>1/2sub>Mn<sub>1/2sub>O<sub>2sub> calcined at 900 °C, a discharge capacity of 92 mAh/g remains after 40 cycles in the voltage range of 1.5–4.0 V, and the Coulombic efficiency remains 100%.