Cyano-Ether Bifunctional Deep Eutectic Electrolytes for Stable Quasi-Solid Lithium Metal Batteries

Lithium metal batteries (LMBs) are promising for high energy density but suffer from safety issues, dendrite growth and interfacial instability. Deep eutectic electrolytes (DEEs) offer potential solutions, yet their practical application is limited by their unsatisfactory interfacial compatibility. This study develops a non-flammable quasi-solid electrolyte for LMBs, via incorporating a novel 3,3'-[oxybis(2,1-ethanediyloxy)]bispropanenitrile (OCN)-based DEE into a poly(butyl acrylate) (PBA) matrix, denoted as OCN-PBA. By integrating both cyano and ether functional groups, the designed OCN molecule enables dual stabilization of both the cathode and anode interfaces, as the cyano group enhances oxidation stability while the ether chains improve lithium compatibility. OCN-PBA possesses a unique aggregated solvation structure, which results in a high ionic conductivity (2.0 × 10^-4 S cm^-1), a Li⁺ transference number (0.66), and a wide electrochemical window (5.0 V). Consequently, Li|OCN-PBA|Li symmetric cell delivers stable plating/stripping over 1500 h, and Li|OCN-PBA|LiFePO₄ cell demonstrates over 2000 stable cycles. Moreover, the OCN-PBA enables excellent cyclic stability in high-voltage Li|LiNi_0.8Co_0.1Mn_0.1O₂ and Li|LiCoO₂ cells. This work proposes a novel electrolyte design strategy, providing a feasible approach for developing practical high-performance LMBs with improved safety.