Theoretical and Kinetic Modeling Investigation of N-Methylpyrrolidone

Abstract

N-methylpyrrolidone (NMP) is essential in lithium-ion battery production. Its thermal decomposition raises concerns regarding the environment, human health, and sustainable battery manufacturing practices. In this work, M062X/6-311++G(d,p) and CCSD(T)-F12a/cc-pVTZ-F12 calculations methods were employed to explore the crucial H-abstraction reactions, bond dissociation energies, and potential energy surfaces of NMP pyrolysis. A comprehensive kinetic model was developed, encompassing 969 species and 5391 reactions, to provide insights into the NMP pyrolysis process. The results reveal that the H-abstraction reactions significantly contribute to NMP decomposition, particularly at lower temperature region within 900-1200 K. The carbon site adjacent to nitrogen atoms on the five-membered ring is found to be more energetically favorable, and the branching ratio of this channel decreases gradually with temperature increasing. As the temperature increases, the effect of the C8 site attenuates gradually, yielding to the C2-H and C11-CH3 sites which emerge as the predominant channels for decomposition, facilitated by H-abstraction reactions by H and CH3 radicals. Rate coefficients of these reactions were determined through RRKM/ME calculations, and the model was validated against available experimental data. Rate-of-production analysis indicates that H-abstraction reactions dominate NMP consumption (over 98%) at 1050 K, playing more important roles than unimolecular decompositions. Sensitivity analysis at 1050 K identifies that CH2NCH2+H=CH3NCH2 and NMP=NMP-11+H have the most obvious inhibiting and promoting effects on NMP consumption, respectively. A promising but under-research study was also identified in present work, along with discussions on their implications for future investigation. By understanding the behavior of NMP during pyrolysis, the battery manufacturing process could be optimized to reduce its environmental impact.

Keywords: Ab initio calculations, Organic solvent, N-methylpyrrolidone, Pyrolysis, Kinetic modeling