Trinitarian Design of Gradient Artificial Interphase Enables Colossal Granular Li Deposits for Stable Li‐Metal Batteries

Abstract The cycling lifespan of Li‐metal batteries is compromised by the unstable solid electrolyte interphase (SEI) and the continuous Li dendrites, restricting their practical implementations. Given these challenges, establishing an artificial SEI holds promise. Herein, a trinitarian gradient interphase is innovatively designed through composite coatings of magnesium fluoride (MgF 2 ), N‐hexadecyltrimethylammonium chloride (CTAC), and polyvinylidene fluoride‐hexafluoropropylene copolymer (PVDF‐HFP) on Li‐metal anode (LMA). Specifically, the MgF 2 /CTAC/PVDF‐HFP SEI spontaneously forms a lithium fluoride (LiF)‐rich PVDF‐HFP‐based SEI, along with lithium‐magnesium (Li‐Mg) alloy substrate as lithiophilic electronic conductor and positively charged CTAC during plating. Noticeably, the Li‐Mg alloy homogenizes the distribution of electric field and reduce the internal resistance, while the electronically insulated LiF/PVDF‐HFP composite SEI offers fast ion‐conducting and mechanical flexibility, accommodating the volumetric expansion and ensuring stable Li‐ion flux. Additionally, CTAC at the dendritic tip is pivotal for mitigating dendrites through its electrostatic shield mechanism. Innovatively, this trinitarian synergistic mechanism, which facilitates colossal granular Li deposits, constructs a dendrite‐free LMA, leading to stable cycling performances in practical Li||LFP, popular Li||NCM811, and promising Li||S full cells. This work demonstrates the design of multifunctional composite SEI for comprehensive Li protection, thereby inspiring further advancements in artificial SEI engineering for alkali‐metal batteries.