Ultralong Cycling of 4.6 V‐Class Lithium Metal Batteries Enabled by a Highly Stable Crosslinked Polymer Deep Eutectic Electrolyte

ABSTRACT Polymer deep eutectic electrolytes (PDEE) often suffer from inadequate electrochemical stability at high voltages (≥4.5 V) and poor interfacial compatibility, which limit their application in high‐voltage lithium metal batteries (LMBs). This study strategically incorporated pentaerythritol triacrylate (PETA) as a crosslinker into a novel polymerizable deep eutectic solvent (PDES) monomer comprising diacetone acrylamide (DAAM), lithium bis (trifluoroethane sulfonyl) imide (LiTFSI), and succinonitrile (SN) to develop a crosslinked polymer deep eutectic electrolyte (Poly (PDES‐CL)). The designed crosslinked polymer network not only promotes lithium salt dissociation through synergistic coordination interactions but also effectively suppresses lithium metal interfacial side reactions. The resulting Poly (PDES‐CL) electrolyte exhibits high ionic conductivity (9.28 × 10 − ⁴ S cm −1 ) and a wide electrochemical window (5.58 V vs. Li⁺/Li). Moreover, the crosslinked polymer network promotes the formation of stable interfaces at both electrodes. As a result, the Poly (PDES‐CL) electrolyte enables ultralong cycling exceeding 5000 h in Li||Li symmetric cells. The LiCoO 2 ||Li cells demonstrate remarkable cyclability, with 97.4% capacity retention after 700 cycles at 4.6 V/ 1C, and 90.4% retention after 1550 cycles at 4.5 V/ 0.5C. Its superior performance in high‐voltage cathode systems ranks it among the top‐performing PDEE, highlighting its potential for high‐voltage LMBs applications.