Adsorption‐Competition Engineered Gradient Self‐Assembled Interphase for Ultra‐Stable Sulfide‐Based All‐Solid‐State Batteries

ABSTRACT Sulfide solid‐state electrolytes (SEs) face severe interfacial instability against lithium metal anodes, leading to detrimental interfacial reactions and rapid degradation. Existing artificial interphases often lack graded functionality to simultaneously block side reactions and guide uniform Li deposition. Herein, guided by theoretical screening of adsorption competition mechanism and interfacial reaction kinetics, we propose a dynamically tailored gradient self‐assembled interphase (SAI) via synergistic reaction of heptafluorobutyric acid (HFA) and fluoroethylene carbonate (FEC) on Li metal surface. The SAI layer features an organic‐rich outer layer, a LiF‐rich intermediate barrier, and a lithiophilic lithium heptafluorobutyrate (LiHFA) inner layer, achieving high interfacial energy, smooth morphology ( R a = 296 nm), and enhanced ion transport. The design enables an ultrahigh critical current density (CCD) of 2.7 mA cm −2 and ultra‐stable cycle over 2000 h at 0.5 mA cm −2 in Li||Li symmetric cells. Moreover, the LiCoO 2 |Li 6 PS 5 Cl|Li full cells with the SAI layer demonstrate remarkable capacity retention of 89.81% after 200 cycles at 0.3 C. This work provides a fundamental thermodynamics‐guided framework for the targeted design of high‐performance interphases in all‐solid‐state Li metal batteries (ASSLMBs).