Investigation of N-Ethyl-2-Pyrrolidone (NEP) as Electrolyte Additive in Regard to Overcharge Protecting Characteristics

Abstract

We report on overcharge protection characteristics of N-ethyl-2-pyrrolidone (NEP) as electrolyte additive. The electrochemical stability of this organic compound was investigated on a platinum working electrode using linear sweep voltammetry. We investigated the overcharge protection effect on a lithium iron phosphate (LFP), a lithium nickel manganese cobalt oxide (NMC) and on a LiMn2O4 (LMO) cathode. Via electrochemical quartz crystal microbalance (EQCMB) measurements the effects of NEP during overcharge were studied and revealed that NEP acts not like a redox shuttle, but is forming a protecting polymeric film. The oxidation products on the cathode were studied by analyzing the surface of the lithium iron phosphate (LFP) and LiMn2O4 (LMO) cathode using XPS spectroscopy.