Tailoring the Bulk Structure and Surface Chemistry of Ni-Rich NCM811 Cathodes via Polyanion Incorporation for Enhanced Electrochemical Performance up to 4.5 V

Abstract

In this study, we investigate the effect of PO<inf>4</inf>3− polyanion incorporation on the physicochemical and electrochemical properties of Ni-rich layered Li(Ni<inf>0.8</inf>Co<inf>0.1</inf>Mn<inf>0.1</inf>)O<inf>2</inf> (P<inf>x</inf>-NCM811, where x = 0.0, 0.3, and 0.5) cathode materials. A coprecipitation method with controlled polyanion injection was employed to ensure homogeneous distribution of PO<inf>4</inf>3− within the precursor particles. Comprehensive structural and morphological analyses confirmed that PO<inf>4</inf>3− incorporation led to reduced primary particle size and the formation of a compact, densely packed microstructure, particularly for the P<inf>0.3</inf>-NCM811 cathode material. X-ray diffraction (XRD) and Rietveld refinement analyses revealed lattice expansion along the c-axis, while X-ray photoelectron spectroscopy (XPS) analysis demonstrated suppressed Ni2+ accumulation and surface stabilization via Li<inf>3</inf>PO<inf>4</inf> formation. Electrochemical evaluation showed that P<inf>0.3</inf>-NCM811 exhibited superior initial discharge capacity (~227 mA h g−1), Coulombic efficiency (~92.7%), rate capability, and cycling stability, with approximately 86.7% capacity retention after 100 cycles at 1.0 C. Electrochemical impedance spectroscopy (EIS) further confirmed lower surface film and charge transfer resistances, as well as enhanced Li+ diffusion kinetics in the polyanion-modified cathodes. Differential capacity analysis indicated improved structural reversibility during phase transitions for P<inf>0.3</inf>-NCM811, with reduced polarization and minimal H2 → H3 transition-induced degradation. These results demonstrate that PO<inf>4</inf>3− polyanion incorporation is a promising strategy to stabilize the structure and improve the electrochemical performance of Ni-rich layered oxide cathodes under high-voltage operation (4.5 V vs. Li/Li+). © © 2025 Youngmin Chi et al. International Journal of Energy Research published by John Wiley & Sons Ltd.