Layered oxides are regarded as highly promising cathode candidates for sodium-ion batteries (SIBs) due to their high-energy density. However, interlayer migration of dopant ions during the charge-discharge cycle process is widely considered detrimental to phase stability and electrochemical activity. Moreover, the origin of this migration and its link to phase transitions and anionic redox reaction (ARR) activity remain unclear due to the insufficient insight into the underlying thermodynamics and dynamics, thereby restricting further application. Herein, the classic ${\mathrm{Na}}_x{\mathrm{Mn}\mathrm{O}}_2$ cathode is taken as an example. From the perspective of lattice dynamics, we demonstrate that it is the soft vibration mode along the out-of-plane direction that triggers the interlayer migration of substituent $\mathrm{Na}$ from the transition metal (TM) layer to the alkali metal (AM) layer, with a low barrier of 0.11 eV/atom. Furthermore, the resulting stable pinning of substituent $\mathrm{Na}$ within the AM layer would act as a “pillar” to stabilize the P2-type layered structure and then effectively mitigate the P-to-O phase transition caused by interlayer sliding during charging-discharging. Moreover, the ARR activity can be effectively enhanced by elevating the $\mathrm{O}$-2p band centers and adjusting the orbital distribution, which is attributed to the formation of $\mathrm{Mn}$ vacancies following interlayer migration. Finally, it is further confirmed via experimental evaluation that the proposed strategy can greatly improve the electrochemical performance of P2-${\mathrm{Na}}_x{\mathrm{Mn}\mathrm{O}}_2$ due to the enhanced ARR activity and minimized structure changes. This study offers pivotal insights into the underlying physical mechanisms that govern ion interlayer migration and its correlation with ARR activity, thereby facilitating the fundamental design of advanced layered oxide cathode materials for SIBs.

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• Density of states
• Electrochemistry
• Solid-solid transformations
• Transport phenomena
• Batteries
• Energy materials
• Layered crystals
• Density functional calculations