Beräkningskemisk modellering för fotoemissionsspektroskopi samt nedbrytningsmekanismer för batterielektrolyter

Abstract

Computational chemical modeling for photoemission spectroscopy and decomposition products of battery electrolytes. The project examines how quantum chemical methods can simulate x-ray photoelectron spectroscopy (XPS) peaks and theoretically analyze decomposition mechanisms for the electrolyte molecules etyhlene carbonate (EC), propylene carbonate (PC) and fluoroet hylene carbonate (FEC) in lithium-ion batteries. By benchmarking quantum chemical methods against experimental data, suitable methods for simulating XPS-spectra and the reaction energetics of the electrolyte decomposition products that balance accuracy and computational cost could be identified. XPS-simulations of ethyltrifluoroacetate (ESCA) show good agreement with experi mental reference data. Simulations of EC and PC were also made, which exhibit good conformity with values within 0.5 eV of the experimental values. These simulations support computational methods as a reliable way of predicting binding-energies. Further on, electrochemical reaction pathways were analyzed with transition state the ory and Marcus theory. The results shows that EC, PC and FEC has similar decompo sition mechanisms in lithium-ion batteries during operation. Additionally, results show that different calculation methods predict different favorable reactions, where Marcus theory generally predicts lower activation barriers and therefore more favorable electron transfer reactions. Explicit transition state calculations tend to predict high activation barriers, especially in ring-opening reaction steps where the reorganization energies are the driving force. It also indicates that FEC has a higher reduction potential and a faster reduction compared to EC and PC, which supports its function as an additive to enhance the solid electrolyte interface (SEI)-formation. In conclusion, this project shows how quantum chemical methods can be versatile in understanding both XPS-spectra and decomposition mechanisms in lithium-ion battery electrolytes with specific usage in analysis of SEI-formation.