Overcoming the energy–durability trade-off in aluminum foil anodes <i>via</i> hierarchical laminated grain boundaries

Aluminum foil anodes offer a lightweight and scalable design by integrating the active material and current collector, but their practical deployment has been limited by rapid mechanical degradation from ∼100% volume expansion during lithiation. Previous strategies to stabilize Al foils have primarily relied on grain refinement, alloying, or prelithiation, which improve either mechanical robustness or electrochemical reversibility, but rarely both. Here, we introduce a fundamentally different microstructural strategy in Al-1 wt% Si foils, where the large atomic size mismatch between Al and Si, combined with the presence of dispersed Si particles, generates pronounced lattice distortions and heterogeneous stored energy that drive the formation of partially recrystallized, laminated grain-boundary architectures. This architecture coordinates grain boundaries: vertical LAGBs/MAGBs guide Li, and periodic horizontal HAGBs drive β-LiAl nucleation and directional growth, forming an alternating α-β lamellar structure during cycling. This laminated α-β network, conceptually akin to a "stack dam" that regulates ion flow and dissipates strain energy, orchestrates phase evolution in a manner distinct from all previously reported Al foil anodes. When coupled with controlled electrochemical prelithiation, this tailored microstructural design fully realizes its potential, simultaneously delivering high energy density and long cycle life.