CeO2-modified P2-Na-Co-Mn-O cathode with enhanced sodium storage characteristics

Abstract

To improve the cycling stability and dynamic properties of layered oxide cathodes for sodium-ion batteries, surface modified P2-Na0.67Co0.25Mn0.75O2 with different levels of CeO2 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 CeO2 surface modification, and a small amount of Ce4+ ions have been reduced to Ce3+ ions, and a few Ce ions have entered the crystal lattice of the P2-oxide surface during modification with CeO2. In a voltage range of 2.0-4.0 V at a current density of 20 mA g-1, 2.00 wt% CeO2-modified Na0.67Co0.25Mn0.75O2 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 CeO2 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.