Multifunctional Electrolytes with Promising Properties via the N-(3-Thienyl)-imidodisulfuryl Fluoride Additive for High-Voltage Graphite/NCM811 Pouch Batteries

An electrolyte additive, N-(3-thienyl)-imidodisulfuryl fluoride (Thienyl-FSI), is rationally designed and synthesized for enhancing the high-voltage and elevated-temperature cycling stability of graphite/LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) pouch cells. Experimental results and theoretical calculations demonstrate that the thienyl-FSI additive preferentially participates in redox reactions at both the cathode and anode, thereby facilitating the formation of uniform, thin electrode-electrolyte interphase (EEI) films that suppress the continuous decomposition of the electrolyte. Furthermore, the cathode electrolyte interphase (CEI) film is abundant with inorganic components (e.g., LiF and Li 2 SO 4 ) and organic polythiophene-based components. This unique composition enables robust CEI films to accommodate volume changes and preserve the structural integrity of the cathode material, resulting in a superior cycling performance in pouch cells. Consequently, commercial pouch cells containing thienyl-FSI exhibit 78% capacity retention after 300 cycles at 25 °C and 77% after 150 cycles at 45 °C within a voltage window of 2.75–4.45 V, compared with a mere 3% for both baseline batteries. This work presents a high-voltage additive, thienyl-FSI, which utilizes bis(fluorosulfonyl)imide to construct a robust EEI and a thienyl skeleton to enhance the high-voltage cycling stability for developing a multifunctional electrolyte, offering a practical strategy for a high-voltage graphite/NCM811 pouch battery.