Interface‐Compatible Deep Eutectic Polymer Electrolytes for High‐Voltage Solid‐State Lithium Metal Batteries

Abstract Polymer electrolytes (PEs) are attractive due to their lightweight, flexibility, facile processability, and intimate solid–solid contact with electrodes for solid‐state lithium‐metal batteries (LMBs). Unfortunately, their practical application is impeded by insufficient ionic conductivity and an unstable electrolyte/electrode interface. Herein, by integrating a butadiene sulfone‐based deep‐eutectic solvent with a fluorinated polymer matrix (PVDF‐HFP), a deep eutectic polymer electrolyte (DEPE) is developed. It is demonstrated that the butadiene sulfone not only liberates lithium ions from the C‐F dipoles in polymer chains, but also establishes a contact‐ion‐pair‐dominated solvation structure, resulting in the DEPE with a high ionic conductivity of 2.1 × 10 ⁻⁴ S cm ⁻¹ at room‐temperature and a lithium‐ion transference number of 0.64. More importantly, the DEPE exhibits outstanding interface compatibility with both the lithium anode and high‐voltage cathode. Benefiting from the weak adsorption of butadiene sulfone on lithium metal, a robust, LiF‐rich solid electrolyte interface is formed at the anode. In addition, its higher HOMO energy level facilitates the formation of a uniform, ‐SO _x ‐rich cathode electrolyte interface on the high‐voltage cathode. As a result, a symmetrical Li||Li cell operates stably for over 1200 h, and full batteries of Li||NCM811 exhibit long‐term cycling stability even at 4.5 V. This study proposes an effective strategy for designing high‐performance PEs, paving the way for the development of high‐voltage, long‐life LMBs.