Localized Anion‐Enriched Environment Via In Situ Electrostatic Confinement Effect for Stable Lithium Metal Batteries

Abstract An anion‐rich electric double layer (EDL) is crucial for promoting the formation of an anion‐derived solid electrolyte interphase (SEI), which significantly enhances the stability of lithium metal anodes. However, during lithium metal deposition, the accumulation of negative charge at the anode surface generates a repulsive electric field, which actively drives anions away from the interface and thereby limits their participation in SEI formation. In this work, a novel strategy is demonstrated to construct an anion‐enriched EDL on the lithium anode under dynamic electrochemical conditions through the “electrostatic confinement effect.” This approach involves introducing dioctadecyl dimethyl ammonium chloride (DODMAC) into the electrolyte system. Upon dissociation, DODMAC yields DODMA + ions that selectively adsorb onto the lithium surface, functioning as molecular anchors to electrostatically attract FSI − anions into the EDL. This mechanism effectively overcomes the anion exclusion caused by the electrode's negative surface charge, enabling the formation of a structurally robust anion‐derived SEI. This phenomenon is termed the “electrostatic confinement effect.” Implementation of this strategy demonstrates significantly enhanced performance in both Li||Cu half‐cell and full‐cell configurations, establishing a direct approach for manipulating EDL composition to optimize SEI architecture in lithium metal batteries.