─a P2-type cathode for sodium-ion batteries─as a well-defined model, we uncover how distinct ion-exchange methods─solid-state ball milling and liquid-phase ultrasonication─induce fundamentally different exchange behaviors via distinct energy-transfer modes. Ball milling drives rapid defect-mediated exchange and a stress-activated 1/5 → 1/3 superstructure transition. In contrast, ultrasonication leads to kinetically limited exchange with intralayer disorder through a collective phonon-like mechanism. Atomic-scale imaging reveals that these contrasting modes give rise to distinct interlayer slip dynamics: short-range stress-driven slip in ball-milled samples and long-range cooperative slip under ultrasonication, both propagating layerwise along aligned ion-diffusion channels. Guided by these mechanistic insights, we develop a sequential ball milling-ultrasonication process that achieves near-complete exchange (98.3 %) within 2 h while retaining the structural integrity. Subsequent postannealing repairs defects and yields a cathode with a reversible capacity of 235 mAh/g (versus lithium metal). This work establishes a rational design framework for efficient, structure-preserving cathode synthesis and reveals general principles governing ion-exchange chemistry in solid oxides.
Ji et al. (2026) studied this question.