Ultra-Thin Lithium Silicide Interlayer for Solid-State Lithium-Metal Batteries.

All-solid-state batteries with metallic lithium (Li ) anode and solid electrolyte (SE) are under active development. However, an unstable SE/Li interface due to electrochemical and mechanical instabilities hinders their operation. Herein, an ultra-thin nanoporous mixed ionic and electronic conductor (MIEC) interlayer (≈3.25 µm), which regulates Li deposition and stripping, serving as a 3D scaffold for Li ad-atom formation, Li nucleation, and long-range transport of ions and electrons at SE/Li interface is demonstrated. Consisting of lithium silicide and carbon nanotubes, the MIEC interlayer is thermodynamically stable against Li and highly lithiophilic. Moreover, its nanopores (<100 nm) confine the deposited Li to the size regime where Li exhibits "smaller is much softer" size-dependent plasticity governed by diffusive deformation mechanisms. The Li thus remains soft enough not to mechanically penetrate SE in contact. Upon further plating, Li grows in between the current collector and the MIEC interlayer, not directly contacting the SE. As a result, a full-cell having Li Si-CNT/Li foil as an anode and LiNi Co Mn O as a cathode displays a high specific capacity of 207.8 mAh g , 92.0% initial Coulombic efficiency, 88.9% capacity retention after 200 cycles (Coulombic efficiency reaches 99.9% after tens of cycles), and excellent rate capability (76% at 5 C).