Development of Property Prediction Methods for Sodium-ion Battery Electrolytes

Student thesis: Masters ThesisMaster of Philosophy

Abstract

In this project, we model the interaction between the sodium ion and the organic solvents, which are widely used in sodium ion batteries (SIBs). The research mainly focuses on how a sodium cation coordinates with the solvent molecules and how its coordination affects the resulting complex structures and infrared vibrations. Three carbonates were used as solvent molecules for this study - propylene carbonate (PC), dimethyl carbonate (DMC) and ethylene carbonate (EC). A larger B3LYP/6-311++G** basis set was used to optimize the geometry and compute the vibrational spectrum of a single molecule EC and its complex including the sodium cation as a benchmark. Both the efficiency and accuracy of ab initio calculations were taken into account for these systems. The coordination of one Na+ with 1–5 solvent molecules were studied using the density functional theory (DFT) method with a smaller basis set B3LYP/6-31G* in the gas phase. The stability of these complexes was then assessed through the determination of their thermodynamic properties. The data obtained confirmed that the four-coordinated complex is the most stable solvation shell structure, which gives a tetrahedral shape. However, results using the larger and more accurate basis set def2-svp suggests that Na+(DMC)3 can be the most stable structure. The accuracy of formed complexes was then assessed by comparing the data obtained from computed infrared spectroscopy with experimental measurements, which clearly demonstrates similar trends by increasing the molar ratio of sodium salts in solution. Finally, the structures generated from the simulation were then also confirmed using NMR measurements.
Date of AwardOct 2017
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorJohan Jacquemin (Supervisor) & Lorenzo Stella (Supervisor)

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