Regulation Mechanism on A Bilayer Li₂O‐Rich Interface between Lithium Metal and Garnet‐Type Solid Electrolytes

Abstract The practical implementation of garnet‐type solid electrolytes, such as Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO), faces the significant challenge of Li dendrites. Though artificial interfacial strategies are effective in dendrite suppression, further investigation is needed to understand the mechanism of homogeneous Li deposition and its practicability under real‐world conditions. Herein, a bilayer interface is constructed to address these issues. Such a bilayer interface consists of one conformal Li 2 O‐rich layer, generated by rubbing LLZTO pellets inside molten Li with low‐dose In 2 O 3 , and another Li 2 O layer deposited through atomic layer deposition (ALD). The regulatory effect of the initial Li 2 O‐rich layer on achieving uniform Li deposition is explored, and the critical current density is enhanced to 2.4 mA cm −2 . However, simple interfacial strategy is insufficient to prevent anodic degradation for cycling at room temperature without stack pressure, leading to increased current leakage and directly reducing Li + within the electrolyte. After insulating it with a second ALD‐Li 2 O layer that minimally hampers ionic conduction, the Li/Li symmetric cells achieve long cycling life exceeding 1000 h at 0.5 mA cm −2 and maintain stable operation even at 2 mA cm −2 . This work provides valuable insights for interfacial strategies towards practical solid‐state batteries.