Abstract
To improve the cycling stability and dynamic properties of layered oxide cathodes for sodium-ion batteries, surface modified P2-Na(0.67)Co(0.25)Mn(0.75)O(2) with different levels of CeO(2) was successfully synthesized by the solid-state method. X-ray photoelectron spectra, X-ray diffraction and Raman spectra show that the P2-structure and the oxidation state of cobalt and manganese of the pristine oxide are not affected by CeO(2) surface modification, and a small amount of Ce(4+) ions have been reduced to Ce(3+) ions, and a few Ce ions have entered the crystal lattice of the P2-oxide surface during modification with CeO(2). In a voltage range of 2.0-4.0 V at a current density of 20 mA g(-1), 2.00 wt% CeO(2)-modified Na(0.67)Co(0.25)Mn(0.75)O(2) delivers a maximum discharge capacity of 135.93 mA h g(-1), and the capacity retentions are 91.96% and 83.38% after 50 and 100 cycles, respectively. However, the pristine oxide presents a low discharge capacity of 116.14 mA h g(-1), and very low retentions of 39.83% and 25.96% after 50 and 100 cycles, respectively. It is suggested that the CeO(2) modification enhances not only the maximum discharge capacity, but also the electric conductivity and the sodium ion diffusivity, resulting in a significant enhancement of the cycling stability and the kinetic characteristics of the P2-type oxide cathode.