Organic Cathode Electrolyte Interphase Achieving 4.8 V LiCoO2

Abstract Developing high‐voltage electrolytes to stabilize LiCoO 2 (LCO) cycling remains a challenge in lithium‐ion batteries. Constructing a high‐quality cathode electrolyte interphase (CEI) is essential to mitigate adverse reactions at high voltages. However, conventional inorganic CEIs dominated by LiF have shown limited performance for high‐voltage LCO. Here, we propose an ionic liquid electrolyte (ILE) with a high donor number additive, enabling Li//LCO cells to achieve a high cut‐off voltage of 4.7 V/4.8 V and a high‐capacity retention of 86.9 %/74.2 % after 100 cycles at 0.5 C. During this process, a groundbreaking phenomenon was discovered: the construction of a stable organic CEI rich in C−F bonds by the high donor number additive under high voltage. These strong polar C−F bonds exhibit excellent electrochemical inertness and film‐forming properties, resulting in optimal passivation of the cathode. This organic C−F bond‐dominated CEI significantly suppresses phase transitions, cobalt dissolution, and gas evolution in LCO at high voltage. Additionally, the 4.8 V‐class Li//LiNi 0.6 Co 0.2 Mn 0.2 O 2 and 4.95 V‐class Li//LiNi 0.5 Mn 1.5 O 4 cells also demonstrate outstanding cycling stability. Even at 60 °C, the ILE‐constructed organic CEI maintains superior performance. Our findings highlight the potential of organic CEI to enhance high‐voltage cathode stability, paving the way for more efficient lithium‐ion batteries.