Solubility Does Not Matter: Engineered Anode Architectures Activates Cost‐Effective Metals for Controlled Lithium Morphology in Li‐Free all‐Solid‐State Batteries

Abstract In Li‐free all‐solid‐state batteries (ASSBs), carbon‐metal composite interlayers are employed, guiding Li deposition at the current‐collector interface. Metals soluble in Li, such as Ag, promote uniform deposition and morphology control of Li. However, unlike in liquid electrolyte systems, most cost‐effective metals fail to achieve similar results as interlayer materials in ASSBs, likely due to limited solubility and mobility in Li. Here, operando optical microscopy reveals that low‐solubility metals like Zn can still induce uniform, dense Li nucleation, although they result in poor morphology and limited cycling stability due to insufficient incorporation into growing Li. This indicates that while lithiophilicity supports nucleation, morphology control requires elaborate contact engineering. To address this, a double‐interlayer architecture is introduced with spatially separated carbon and Zn layers, deliberately guiding Li deposition at the carbon|Zn interface. This configuration enables the effective utilization of Zn in forming contact with Li deposits despite its low solubility, resulting in dense, vertically‐aligned Li growth and significantly enhanced performance—76.7% capacity retention over 400 cycles at 0.33C, with 99.89% coulombic efficiency in pouch cells under practical pressure (2 MPa). This approach provides a versatile, universally applicable platform for activating low‐ or non‐soluble metals like Al, Sn, and Bi beyond costly Ag.