Lithium-rich manganese-based layered oxides are promising cathode materials for next-generation lithium-ion batteries, offering exceptionally high energy densities through combined transition metal and oxygen redox. However, this high energy density presents a critical limitation: these materials suffer progressive loss of energy density upon cycling, due to progressive decrease in average voltage; a phenomenon termed ‘voltage fade’ [1–4]. Understanding and controlling the underlying mechanisms of voltage fade are essential to realise the full potential of these high-capacity cathode materials.

Voltage fade has been linked to the formation and growth of nanoscale voids within the cathode bulk [1], but the atomic-scale mechanisms of this process are not well understood. The conventional approach for modelling battery cathode materials at the atomic scale is density functional theory (DFT). However, DFT cannot be used to directly investigate nanoscale void formation and growth, because the necessary system sizes are too large to be computed.

To investigate void formation over extended cycling, we have developed a novel computational approach combining DFT calculations, cluster expansion models, and Monte Carlo simulations. By applying this methodology to Li-rich Mn-based cathodes across the Li₂MnO₃–LiMnO₂ compositional space, we find that nanoscale voids form through two concurrent processes: formation of O₂ molecules within the bulk and extensive transition metal migration that forms transition-metal-deficient regions via phase segregation. Under extended cycling, these voids coalesce, driven by surface energy minimisation, in a process analogous to Ostwald ripening.

We further find that void coalescence—and thus voltage fade—depends strongly on the initial Mn/Li configuration in the Mn-rich layer, suggesting that targeting specific initial structures can inhibit deleterious structural evolution during cycling. By establishing the direct link between void growth and voltage loss, we show that preventing coalescence offers a route to maintaining electrochemical performance. Through systematic mapping of voltage fade across the Li₂MnO₃–LiMnO₂ compositional space, we identify optimal structures and compositions that minimise degradation whilst retaining high energy density. These findings establish clear structural and compositional design principles for developing Li-rich cathodes with sustained performance over extended cycling.

[1] McColl, K.; Coles, S. W.; Zarabadi-Poor, P.; Morgan, B. J.; Islam, M. S. Phase Segregation and Nanoconfined Fluid O₂ in a Lithium-Rich Oxide Cathode. Nat. Mater. 2024, 23, 826−833.

[2] Csernica, P. M.; McColl, K.; Busse, G. M.; Lim, K.; Rivera, D. F.; Shapiro, D. A.; Islam, M. S.; Chueh, W. C. Substantial Oxygen Loss and Chemical Expansion in Lithium-Rich Layered Oxides at Moderate Delithiation. Nat. Mater. 2025, 24, 92−100.

[3] House, R. A.; Rees, G. J.; McColl, K.; Marie, J. J.; Garcia-Fernandez, M.; Nag, A.; Zhou, K.-J.; Cassidy, S.; Morgan, B. J.; Islam, M. S.; Bruce, P. G. Delocalized Electron Holes on Oxygen in a Battery Cathode. Nat. Energy 2023, 8, 351−360.

[4] McColl, K.; House, R. A.; Rees, G. J.; Squires, A. G.; Coles, S. W.; Bruce, P. G.; Morgan, B. J.; Islam, M. S. Transition Metal Migration and O₂ Formation Underpin Voltage Hysteresis in Oxygen-Redox Disordered Rocksalt Cathodes. Nat. Commun. 2022, 13, 5275.