Front-Loading Zn²⁺ via Lattice-Breathing-Enabled Early-Stage Co-Intercalation for Ultrastable Zn-Ion Batteries

Manganese oxide cathodes for aqueous zinc-ion batteries present a fundamental performance dichotomy, where the rapid kinetics of H⁺ insertion are offset by structural degradation through acidification and manganese dissolution, whereas the more structurally compatible Zn²⁺ insertion is hindered by sluggish diffusion and severe lattice strain. This conventional trade-off, stemming from the sequential or competitive nature of these ion-storage pathways, has long constrained the achievable capacity and cycling stability. Here, we report that In³⁺ incorporation into δ-MnO₂ creates a dynamically adaptive lattice through controlled local strain fields, activating effective transport pathways for ultrafast charge propagation. Crucially, multimodal characterization reveals an unconventional ion-storage mechanism in which the In³⁺-modified host enables concerted Zn²⁺/H⁺ co-insertion initiating at the onset of discharge. This front-loaded co-intercalation mechanism, facilitated by the breathing framework, ensures efficient charge compensation while minimizing deleterious H⁺-dominant processes, thereby preserving crystallographic integrity. Consequently, the In-δ-MnO₂ cathode exhibits exceptional kinetics with significantly reduced ion-migration barriers, delivering a high specific capacity of 310.6 mAh g^-1 at 0.5 A g^-1 and sustaining 25 000 cycles with minimal decay at 5 A g^-1. This work establishes dynamic lattice breathing as a generalizable design principle to reconcile fast ion transport with structural reversibility.