Fluorination-promoted structural evolution and enhanced electrochemical performance in low Li-excess manganese-based cation-disordered rocksalt cathodes

Cation-disordered rocksalt (DRX) oxides have emerged as attractive candidates for high-capacity lithium-ion battery cathodes, owing to their flexible compositional tunability and potential to access both cationic and anionic redox. However, practical application is hindered by oxygen redox instability and sluggish Li + transport, especially in highly lithium-excess systems. In this study, we investigate fluorine-substituted Mn-based DRX cathode with low lithium excess (Li 1.1 Mn 0.7+ x Ti 0.2− x O 2−  x F x ), designed to reconcile the trade-off between Li + diffusion and structural stability. Systematic structural and electrochemical analyses reveal that fluorine doping suppresses oxygen redox activity by boosting the redox capacity contribution by increasing the Mn content. Most notably, fluorine substitution promotes phase transformation from disordered rocksalt to spinel-like domains during cycling via enhanced Mn migration, which in turn significantly enhances Li + transport kinetics. The optimized Li 1.1 Mn 0.8 Ti 0.1 O 1.9 F 0.1 cathode delivers a maximum discharge capacity of 228.7 mAh g − ¹ at 0.1 C and retains 115.4 mAh g −1 at 2 C, outperforming its undoped counterpart (Li 1.1 Mn 0.7 Ti 0.2 O 2 : 203.2 mAh g −1 at 0.1 C; 81.0 mAh g −1 at 2 C). These findings provide the dual role of fluorination in structural tuning and redox modulation, offering a new strategy to optimize low lithium-excess DRX systems through controlled fluorination and phase engineering. Graphical