Dual-functional additives enabling a high-performance silicon–carbon composite anode in pouch cells at high temperatures

Abstract

Silicon–carbon composite (Si–C) is currently the most promising anode material for lithium-ion batteries (LIBs) due to its high energy density. However, the large volume change of Si particles during cycling causes sustained damage to the solid electrolyte interface (SEI), leading to deterioration of cycling performance, especially at high temperatures. In this study, fluoroethylene carbonate (FEC) and succinic anhydride (SA) were employed as dual-functional additives to improve the cycling performance of the Si–C anode at high temperatures. High-energy-density LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811)/(Si–C) pouch cells were assembled to evaluate the performance of the dual-functional additives. It is found that an appropriate amount of FEC improved the cycling stability of pouch cells at room temperature by facilitating the formation of LiF-rich SEI. However, this improvement failed at high temperatures due to the triggering of massive side reactions. The incorporation of both FEC together and SA effectively solved this problem and improved the cycling and storage performance of pouch cells at high temperatures by forming a uniform and dense Li₂CO₃-rich SEI film, which provided good thermal stability. Density functional theory calculations and ultrasound transmission imaging were used to illustrate the mechanism. All data were collected at pouch cell level, making the findings more persuasive.