Phonon‐Driven Insights Into Layer Sliding of High‐Voltage Layered Cathode

Understanding the structural instability of high‐voltage layered cathodes remains a critical challenge in advancing sodium‐ion batteries. In particular, the mechanism of slab gliding, a key contributor to phase transitions, has not been fully elucidated at the atomic level. Here, we propose a breathing‐shear mode coupling model based on the phonon spectrum, which elucidates the slab gliding mechanism in layered cathode materials by using interlayer spacing as the order parameter. Employing a “single‐layer to double‐layer” comparative strategy in P2‐Na 0 MnO 2 , we establish a direct link between specific phonon modes and atomic‐scale dynamics. This mode corresponds to a C‐glide vibration, which features cooperative atomic motion within the layers and relative sliding between adjacent layers. Due to its negative vibrational energy, this mode drives exponential atomic displacement and triggers structural transformation. Notably, van der Waals‐corrected phonon analysis reveals that weak interlayer interactions enhance this dynamic instability. Finally, we propose a solution to control structural stability by adjusting the interlayer spacing on the basis of phonon spectrum analysis. This phonon mode‐stability correlation framework offers new theoretical guidance for designing robust high‐voltage layered cathodes.