( Invited ) “Lithium-Free” Anode Solid-State Batteries Enabled by 3D Structured Mixed Ionic Electronic Conducting Garnet

We demonstrate a mechanistic pathway for electronic percolation within a mixed ionic and electronic conducting (MIEC) garnet scaffold that enables “Li-free” anode solid-state batteries with dramatically reduced anode impedance and previously unheard of Li metal cycling efficiency. The porous MIEC layer spontaneously nucleates a conformal nm-scale Li metal film providing an electronic pathway that achieves a dramatic reduction in impedance at lithium volume fractions <1%, significantly increasing available cell cycling capacity. Moreover, “Li-free” (MIEC(P)-LLZ(D)-MIEC(P)) trilayers achieve Li metal stripping/plating coulombic efficiency as high as 99.995 % at 1 mA/cm 2 . When paired with NMC811 cathodes, bilayer (MIEC(P)-LLZ(D)) “lithium-free” full cells exhibit stable, highly reversible cycling at practical current densities, all at room temperature with no applied pressure. The interplay between lithium volume fraction and impedance is quantitatively modeled, transforming the understanding of lithium nucleation in a “lithium-free” cell from an empirical interface problem to a percolation-governed transport process, guiding the design of electronically percolating scaffolds for next-generation solid-state batteries.