posted on 2023-12-08, 22:00authored byMingzu Liu, Min Li, Bolun Zhang, Houmou Li, Jiaxin Liang, Xinyu Hu, Haimei Liu, Zi-Feng Ma
Due to its low cost and high stability,
the iron-based mixed polyanionic
compound Na4Fe3(PO4)2P2O7 is widely studied for use as a sodium-ion battery
cathode material. However, its development is limited by a low electrical
conductivity and restricted diffusion kinetics. In this work, we chose
to replace the PO43– group with the SiO44– group to enhance the electronic conductivity
and diffusion kinetics, while this structural substitution maintains
the integrity of the material. Furthermore, this substitution at a
nonactive site improves the electrochemical performance without reducing
the theoretical capacity. Additionally, it stabilizes the crystal
structure during the repeated charging and discharging process. As
a result, this SiO44– doped Na4Fe3(PO4)2P2O7 exhibits improved electrochemical properties. For instance, it achieves
a capacity of 119.4 mA h g–1 at a rate of 0.1 C
and 60.7 mA h g–1 at 50 C after 5000 cycles with
84.2% of its capacity retained. Moreover, theoretical calculations
revealed the doping form and occupancy of SiO44– in the host material structure. It is believed that this work provides
a new perspective on doping modification with anionic groups to improve
the electrochemical performance of cathode materials for sodium ion
storage.