Enabling an Inorganic-Rich Interface via Cationic Surfactant for High-Performance Lithium Metal Batteries

An anion-rich electric double layer (EDL) region is favorable for fabricating an inorganic-rich solid-electrolyte interphase (SEI) towards stable lithium metal anode in ester electrolyte. Herein, cetyltrimethylammonium bromide (CTAB), a cationic surfactant, is adopted to draw more anions into EDL by ionic interactions that shield the repelling force on anions during lithium plating. In situ electrochemical surface-enhanced Raman spectroscopy results combined with molecular dynamics simulations validate the enrichment of NO₃^-/FSI^- anions in the EDL region due to the positively charged CTA⁺. In-depth analysis of SEI structure by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry results confirmed the formation of the inorganic-rich SEI, which helps improve the kinetics of Li⁺ transfer, lower the charge transfer activation energy, and homogenize Li deposition. As a result, the Li||Li symmetric cell in the designed electrolyte displays a prolongated cycling time from 500 to 1300 h compared to that in the blank electrolyte at 0.5 mA cm^-2 with a capacity of 1 mAh cm^-2. Moreover, Li||LiFePO₄ and Li||LiCoO₂ with a high cathode mass loading of > 10 mg cm^-2 can be stably cycled over 180 cycles.