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

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.