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–Na_0.67Co_0.25Mn_0.75O₂ 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 Na_0.67Co_0.25Mn_0.75O₂ 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.