Organic Cathode Electrolyte Interphase Achieving 4.8 V LiCoO2.

Abstract

Developing high-voltage electrolytes to stabilize LiCoO2 (LCO) cycling remains a challenge in lithium-ion batteries. Constructing a high-quality cathode electrolyte interface (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//LiNi0.6Co0.2Mn0.2O2 and 4.95 V-class Li//LiNi0.5Mn1.5O4 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.