Oxidation stability of N-ethyl-2-pyrrolidinone under high voltage environments

Abstract

This work was aimed at investigating the electrochemical oxidation behavior of poly(vinylpyrrolidone) (PVP, a popular dispersant in the process of battery production) under high voltage environments. N-ethyl-2-pyrrolidone (NEP) was selected as a compound representative of PVP. Working electrodes were designed and prepared with a mixture of NEP and ethylene vinyl alcohol (EVOH) as a vehicle, and conductive carbon black as the electron transport material. Linear sweep voltammetry (LSV) was used to monitor the reactions underwent by NEP. The oxidative products were analyzed with X-ray photoelectron spectroscopy (XPS) and gas chromatography coupled with mass spectrometry (GC–MS). LSV revealed electrochemical oxidation of NEP taking place at voltages higher than 4 V. XPS and GC–MS revealed that the electrochemical oxidative products contained an ammonium group derived from the loss of electrons of the NEP under the electric field. Two types of ammonium species were identified: (i) species resulting from the loss of four electrons followed by hydrolysis and; (ii) species of higher molecular weight as a result of the replacement of ethyl group on NEP with methoxy (from lithium methoxide) followed by loss of protons and electrons (two-electron-two-proton process) with hydrogen being exchanged with fluorine. A reasonable mechanism was proposed to explain these results.