Unilateral‐Cyano‐Functionalized Asymmetric Ether‐Based Electrolytes Enable Stable High‐Voltage Lithium Metal Batteries

ABSTRACT Enhanced demand for high‐energy‐density batteries has intensified the focus on high‐voltage Ni‐rich ternary cathodes. However, their high‐voltage characteristics are challenging to match the narrow electrochemical stability window of traditional ether electrolytes. Herein, we propose a series of unilateral‐cyano‐functionalized asymmetric glyme (glyme‐CN) electrolytes with broadened oxidation stability by molecular engineering. The electron‐withdrawing cyano group enhances oxidation stability by suppressing ether‐oxygen lone pair loss, while their solvation structures are finely tuned to promote anion‐derived interfacial chemistry. The optimized electrolyte glyme‐CN named TF achieves a 5.2 V electrochemical stability window, 98.9% Coulombic efficiency in Li||Cu cells, and stable cycling in Li||Li cells over 1400 h. The Li||LiFePO 4 full battery with electrolyte TF delivers remarkable cycling stability, maintaining 133.3 mAh g −1 high capacity with a 90.8% capacity retention rate after 4000 cycles at 1C. Furthermore, TF enables a 4.3 V LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode to retain 64.2% capacity after 800 cycles and sustains stable operation even at 4.6 V. This precise molecular engineering strategy for structure and property customization provides new insights into the development of advanced battery materials.