Dual‐Layer Solid Electrolyte Interphase Enables Effective Suppression of Lithium Dendrites

The heterogeneous solid electrolyte interphase (SEI) at the Li metal anode often leads to slow and uneven Li + flux, causing severe Li dendrite growth. Herein, we combine X‐ray photoelectron spectroscopy and cryogenic transmission electron microscopy to demonstrate that a dual‐layer SEI, consisting of an inorganic inner layer and an organic outer layer, is suitable to achieve uniform deposition of Li metal anodes. Through theoretical calculations, we propose a novel parameter, bond dipole moments, to describe the decomposition mechanism of liquid electrolytes and the subsequent formation of the dual‐layer SEI. Consequently, the optimal dual‐layer SEI, comprising a uniformly distributed, highly ion‐conductive nanoparticle inner layer and a high‐molecular‐weight polymer outer layer, achieves ultrahigh reversibility of the Li metal anode. The Li||Cu cell achieved a high Coulombic efficiency of 99.5% over 300 cycles at a current density of 1.0 mA cm −2 , and a 3‐Ah Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 pouch cell delivers an energy density of 424 Wh kg −1 with a stable lifespan of 153 cycles.