Systematic Investigation of Alkali Metal Ions as Additives for Graphite Anode in Propylene Carbonate Based Electrolytes

Propylene carbonate (PC) is an electrolyte co-solvent with a wide working temperature range, which can improve the performance of lithium ion batteries (LIBs). Unfortunately, PC co-intercalates into graphite with lithium ions leading to exfoliation and rapid capacity decay. Incorporation of low concentrations of Cs+ or K+ ions as additives improves the performance by inhibiting graphite exfoliation and leading to better first cycle efficiency. The electrochemical behavior of graphite anodes with a series of electrolytes containing added alkaline metal acetate salts, Li, Na, K, and Cs, has been investigated. Cells containing K and Cs acetate have the highest first cycle efficiency and reversible cycling capacity. In an effort to better understand the role of the cation on performance, the solid electrolyte interphase (SEI) on the graphitic anodes cycled with the different electrolytes has been investigated via a combination of X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Infrared Spectroscopy (ATR-IR), Transmission electron microscopy (TEM) and Inductive coupled plasma mass spectrometry (ICP-MS). The presence of the heavier cations (K and Cs) leads to a thinner SEI with higher LiF content which is likely responsible for the performance enhancement.