Fatigue-Free and Skin-like Supramolecular Ion-Conductive Elastomeric Interphases for Stable Lithium Metal Batteries

The heterogeneity and continuous cracking of the static solid electrolyte interphase (SEI) are one of the most critical barriers that largely limit the cycle life of lithium (Li) metal batteries. Herein, we report a fatigue-free dynamic supramolecular ion-conductive elastomeric interphase (DSIEI) for a highly efficient and dendrite-free lithium metal anode. The soft phase poly(propylene glycol) backbone with loosely Li⁺-O coordinating interaction was responsible for fast ion transport. Simultaneously, the supramolecular quadruple hydrogen bonds (H-bonds) in the hard phases endow the elastomeric interphase with mechanical enhancement, while gradient H-bonds can dissipate strain energy via the sequential bonding cleavage. Such a design affords superior mechanical robustness, high ionic conductivity, gradient energy dissipation, and high Li⁺ transference number. Besides, anion enrichment in DSIEI assists in situ construction of a lithium fluoride-rich inner layer upon cycling. The resultant biomimetic bilayer structure enables the symmetric cells with superior cyclability of over 600 h at a high current density of 10 mA cm^-2. Moreover, the DSIEI allows stable operation of the full cells under constrained conditions of limited lithium excess, a high-loading LiNi_0.8Co_0.1Mn_0.1O₂ cathode, and a low negative/positive capacity (N/P) ratio. This work presents a powerful strategy for deigning artificial SEI and achieving high-energy-density Li metal batteries.