Localized introduction of zirconium in P2 sodium layered oxide electrode for high capacity sodium-ion battery

Abstract

The Na0.67[Ni0.3Mn0.5Fe0.2]1-xZrxO2 (x = 0, 0.05, 0.075 and 0.1, respectively) materials composed of eco-friendly elements was synthesized via the sol-gel method. The X-ray diffraction (XRD) patterns demonstrated that all of the samples have a typical P2-type structure. The Na0.67[Ni0.3Mn0.5Fe0.2]0.95Zr0.05O2 exhibited the smaller lattice parameter a and b (a = b in P2 type), whereas the larger parameter c. The physical characterization of the materials showed that the Zr element was present in the form of zirconia and Zr doping. The pristine P2-Na0.67Ni0.3Mn0.5Fe0.2O2 delivers excellent electrochemical performance with an initial discharge specific capacity of 235.3 mA h g−1 (corresponding to 98.4% of the theoretical capacity) at a rate of 0.1 C between 1.5 and 4.3 V. The cycle performance of Na0.67[Ni0.3Mn0.5Fe0.2]0.95Zr0.05O2 is substantially improved compared with Zr free Na0.67Ni0.3Mn0.5Fe0.2O2, delivers a retention capacity increased from 40.5% to 56.2% after 100 cycles with 207.7 mA h g−1 in the 1st cycle. Combined with system analysis including the Transmission Electron Microscopy (TEM) and electrochemical methods, the better electrochemical performance can be attributed to the phase transformation suppression and the improvement of sodium diffusion kinetics brought about by the introduction of zirconium. The favorable Na storage performance of full cell with Na0.67[Ni0.3Mn0.5Fe0.2]0.95Zr0.05O2 cathode material paves the way for high capacity sodium-ion battery.