Fig. 5: Ex situ cryogenic FIB-SEM measurements of Al_94.5In_5.5 and aluminum foils at different stages of cycling in SSBs.

a Pristine aluminum, b aluminum after full lithiation, and c aluminum after delithiation. d Pristine Al_94.5In_5.5, e Al_94.5In_5.5 after LiIn formation, f Al_94.5In_5.5 after full lithiation, and g Al_94.5In_5.5 after delithiation. All cells for FIB-SEM were assembled with a stack pressure of 50 MPa and cycled at 0.7 mA cm⁻² with positive electrode loading of 3.0 mAh cm⁻², with both sets of foils being 11 μm in thickness instead of the 30 μm-thick foils used elsewhere to ensure FIB milling effectiveness. The red dotted lines in all images outline the cross-section. All testing was performed at 25 °C. h–k Schematics showing reaction mechanisms in the Al–In foil with a multiphase microstructure. h Pristine Al–In foil in contact with SSE. i The distributed indium phase is lithiated first to form LiIn. j The aluminum phase begins to react with lithium transported from the LiIn phase. k During delithiation, the LiIn phase remains lithiated and can transport lithium to avoid trapping by the pure aluminum phase.