Insights into the Bulk Structure and Redox Chemistry of Li₂NiO₃—A Lithium Rich Nickel Oxide Cathode Material

The advancement of Li ion batteries in energy storage technologies fosters the need to develop high performance cathode active materials that assure impressive energy densities with prolonged cyclability and low expense. Nickel oxides have garnered significant interest in this regard owing to accessible high voltages and capacities and ready availability of nickel¹. An unavoidable caveat with Ni rich systems is their susceptibility to structural instabilities that propel degradation during the battery charge-discharge cycles.<br/>Amongst several promising compounds in the Li-Ni-O chemical space, we focus on Li₂NiO₃ or Li[Ni_2/3Li_1/3]O₂ – the most Li rich member in the Li_1+yNi_1-yO₂ solid solution, inspired by recent reports highlighting its synthesizability and attractive first cycle capacity ^2,3. It does, however, suffer from a quick capacity fade which has been attributed to anionic redox and oxygen release.<br/>As the anionic sublattice is of high significance in layered oxide materials, it is imperative to devise a correlation between oxygen redox and the bulk structure of Li₂NiO₃^4,5. Structural uncertainties are manifested in the form of oxygen deficiencies (Li₂NiO_{3 -δ}) and Ni/Li mixing, as observed from ICP analyses and neutron powder diffraction studies². While the oxygen deficiencies influence the Ni oxidation state and hence the underlying electronic structure, the cationic site disorder results in an imperfect honeycomb ordering leading to stacking faults.<br/>Employing a systematic computational approach,^6,7 with hybrid Density Functional Theory studies, our work probes the defect configurational landscape in Li₂NiO_{3 -δ} . It reveals the importance of an accurate representation of the bulk structure at the charged and partly lithiated states, as a keystone for possible routes of structural transformation and draws a connection between the evolution of electron holes and the reversibility of oxygen redox.<br/><br/><br/>References :<br/>1. W. Li, E. M. Erickson, A. Manthiram, <i>Nat. Ener.</i> (2020), 5, 26-34<br/>2. M. Bianchini, A. Schiele, S. Schweidler, S. Sicolo, F. Fauth, E.Suard, S. Indris, A. Mazilkin, P. Nagel, S. Schuppler, M. Merz, P. Hartmann, T. Brezesinski, J. Janek, <i>Chem. Mater.</i> (2020), 32, 9211−9227.<br/>3. J. Cen, B. Zhu, D. O. Scanlon, .<i>J. Phys. Energy </i>(2023), 5, 035005.<br/>4. R. A House, U, Maitra, M. A Perez-Osorio, J.G. Lozano, J.W. Somerville, L. C. Duda, A. Nag, A. Walters, K-J Zhou, M. Roberts, P.G. Bruce, <i>Nature </i>(2020), 577, 502-508.<br/>5. R. A. House, G. J. Rees, K. McColl, J-J Marie, M Garcia-Fernandez, A. Nag, K-J Zhou, S. Cassidy, B. J. Morgan, M.S Islam, P.G. Bruce, <i>Nat. Ener.</i>, (2023), 8, 351-360.<br/>6. S.R. Kavanagh, A.G. Squires, A. Nicolson, I. Mosquera-Lois, A. M Ganose, B.Zhu, K. Brlec, A. Walsh, D.O.Scanlon; <i>Journal of Open Source Software</i>, 2024, 9(96), 6433<br/>7. I Mosquera-Lois, S.R. Kavanagh, A. Walsh, D.O.Scanlon, <i>npj Comp. Mater.</i>, (2023), 9, 25.