Investigations on the electrochemical decomposition of the electrolyte additive vinylene carbonate in Li metal half cells and lithium ion full cells

In this study, the decomposition of vinylene carbonate (VC) additive and its effect on the aging behavior is investigated in Li metal half cells and lithium ion full cells. Four electrolyte systems, the reference electrolyte with three VC additive amounts, i.e., 1, 5 and 10 vol% are examined with commercial LiNi1/3Mn1/3Co1/3O2 (NMC 111) cathode material and mesophase carbon microbeads (MCMB) anode material. The thickness changes of the cathode electrolyte interphase (CEI) and of the solid electrolyte interphase (SEI) after 5 constant current cycles at 0.1C and 200 constant current/constant voltage (potential) cycles at 1C are investigated for cells containing different amounts of VC. With the help of X-ray photoelectron spectroscopy (XPS) and high-performance liquid chromatography (HPLC), a correlation between CEI thickness change and electrolyte decomposition is figured out. The addition of VC leads to a thin CEI layer and a high capacity retention in a lithium metal half cell. A strong dependence of the performance on the VC concentration is found for half cells that results from the continuous consumption of electrolyte and the electrolyte additive at the Li metal counter electrode. In contrast, for full cells, even 1 vol% of VC helps to form both a stable CEI and SEI, while a larger amount of VC increases the CEI thickness, electric contact loss and the internal resistance.