Utilizing a Novel Electrolyte Additive for Improvement of the Solid Electrolyte Interphase on Silicon Anodes of Lithium-Ion Batteries

Abstract

Graphite is currently the most widely used anode material in lithium-ion batteries due to its layered structure and long cycling stability. However, any lithium-ion batteries built with graphite are inherently limited by graphite’s moderate theoretical capacity of 372mAh/g and subsequent low energy density. A more promising anode material is silicon due to its significantly higher theoretical capacity of 3579mAh/g, creating a much higher energy density. Unfortunately, silicon experiences large volume changes during cycling that causes the pulverization of active materials, thus fracturing the electrode surface and reducing electrical conductivity. The constant morphology changes furthermore damage the formation of a stable solid electrolyte interphase (SEI) on the silicon particles, causing continuous consumption of electrolyte and thickening of the SEI layer. These all contribute to rapid capacity decay and short cycle life. One way to improve the cycling performance of silicon anodes is to include electrolyte additives like fluoroethylene carbonate (FEC) that preferentially reduce on the surface of the anode. These additives enable the ability to develop a more robust and flexible passivation film that can accommodate electrode expansion. In this study, a novel electrolyte additive formulation was used to improve the long-term cycling stability of silicon anode half cells. The resultant SEI layer was characterized using X-ray photoelectron spectroscopy and attenuated total reflectance infrared spectroscopy as well as examined using scanning electron microscopy for morphology changes.