Detailed Structural and Electrochemical Comparison between High Potential Layered P2-NaMnNi and Doped P2-NaMnNiMg Oxides

Rechargeable sodium-ion batteries are viable candidates as next generation energy storage devices. Nonetheless, the development of high-potential and stable cathode materials is still one among the open tasks. Here, we propose a combined experimental/theoretical approach to shed light on the effect of magnesium doping on the layered P2-Na0. 6 7Mn0.75Ni0.25O2 cathode material. The P2Na0.67Mn0.75Ni0.25O2 baseline material and doped P2-Na0.67Mn0.75Ni0.20Mg0.05O2, synthesized via coprecipitation route followed by thermal treatment, have been physically and chemically characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), as well as electrochemically via galvanostatic cycling and galvanostatic intermittent titration technique (GITT). The Mg-doped material showed stabilization of the high potential plateau and improved cycle life. The analysis of the phase transition with synchrotron operando XRD (SXRD) shows multiple possible intermediate phases (Z-phase) rather than a pure OP4-like structure. Based on our experimental data and periodic density functional theory (DFT) calculations, the stability of the O2, P2, and OP4 phases for the pristine and Mg-doped systems was investigated to elucidate the origin of the Z phase formation in the Mg-doped material.

Automated summary

This study proposes a combined experimental/theoretical approach to investigate the effect of magnesium doping on the performance of sodium-ion battery cathode materials. The results show that magnesium doping improves the stability of the high potential plateau and enhances the cycling life. The analysis also reveals the presence of multiple possible intermediate phases in the magnesium-doped material.