High-Energy Ni-Rich LiNi_0.85Co_0.1Mn_0.05O₂Cathode Material for Li-Ion Batteries Enhanced by Nd- and Y-Doping. A Structural, Electrochemical, and Thermal Investigation

Ni-rich LiNi_1-x-yCo_xMn_yO₂(1 - x - y > 0.5) (NCMs) cathode materials have shown great promise in energy-intensive applications, such as electric vehicles. However, as many layered cathodes do, they suffer from structural and electrochemical degradation during cycling. In this study, we show that Nd- and Y-doped materials, Li(Ni_0.85Co_0.1Mn_0.05)_0.995Nd_0.005O₂and Li(Ni_0.85Co_0.1Mn_0.05)_0.995Y_0.005O₂, have significantly better structural, electrochemical, and thermal properties compared to the reference LiNi_0.85Co_0.1Mn_0.05O₂(NCM85) due to enhanced structural stability. The doped electrodes were found to have significantly higher specific discharge capacities, better capacity retention, and lower voltage hysteresis compared to the reference (undoped) electrodes. SEM images of the focused-ion beam (FIB) cut of the particles of the doped material showed that they have less cracks when compared with those of the reference material, thus demonstrating the tight connection between the structural and electrochemical properties of the cathodes. Furthermore, thermal studies of the cathode materials showed that doping with Nd or Y enhances the thermal stability of NCM85 compared to the reference material. Finally, using density functional theory we calculated several electronic and thermodynamic properties. These calculations suggest that dopant-oxygen bonds are stronger than M-oxygen bonds (M = Ni, Co, Mn), providing a rationale for the structural stability induced by Nd- and Y-doping.