Ultra‐tough Dynamic Supramolecular Ion‐conducting Elastomer Induced Uniform Li+ Transport and Stabilizes Interphase Ensures Dendrite‐free Lithium Metal Anodes

Artificial polymer solid electrolyte interphases (SEIs) with microphase‐separated structures provide promising solutions to the inhomogeneity and cracking issues of natural SEIs in lithium metal batteries (LMBs). However, achieving homogeneous ionic conductivity, excellent mechanical properties, and superior interfacial stability remains challenging due to interference from hard‐phase domains in ion transport and solid‐solid interface issues with lithium metal. Herein, we present a dynamic supramolecular ion‐conducting poly(urethane‐urea) interphase (DSIPI) that achieves these three properties through modulating the hard‐phase domains and constructing a composite SEI in situ. The soft‐phase polytetrahydrofuran backbone, featuring loose Li+‐O coordinating interactions, ensures uniform Li+ transport. Concurrently, sextuple hydrogen bonds in the hard phase dissipate strain energy through sequential bond cleavage, thereby imparting exceptional mechanical properties. Moreover, enriched bis(trifluoromethanesulfonyl)imide anion (TFSI‐) in DSIPI promotes the in‐situ formation of a stable polymer‐inorganic composite SEI during cycling. Consequently, the DSIPI‐protected lithium anode (DSIPI@Li) enables symmetric cells with exceptional cyclability exceeding 4,000 hours at an ultra‐high current density of 20 mA cm‐2, thereby demonstrating excellent cycling stability. Furthermore, DSIPI@Li facilitates stable operation of the pouch cells under the constraints of a high‐loading LiNi0.8Co0.1Mn0.1O2 cathode and low negative/positive capacity (N/P) ratio. This work presents a powerful strategy for designing artificial SEIs and high‐performance LMBs.