Structures and dynamic properties of the LiPF₆ electrolytic solution under electric fields - a theoretical study

Area of Science:

• Electrochemistry
• Materials Science
• Computational Chemistry

Background:

• High-voltage lithium ion batteries require advanced electrolytes.
• Fluorinated carbonates are promising candidates due to their stability.
• Dynamic solvent properties under electric fields are critical but understudied.

Purpose of the Study:

• To investigate the structure-related dynamic properties of fluorinated carbonates.
• To simulate solvent behavior under both free and electric field conditions.
• To understand the impact of fluorine content on electrolyte performance.

Main Methods:

• Joint Molecular Dynamics (MD) and Density Functional Theory (DFT) calculations.
• Simulation of linear fluorinated carbonate solutions.
• Prediction of dielectric constants, solvation energies, viscosity, and ion mobility.

Main Results:

• Dielectric constants range from 5.4 to 12.1, dependent on fluorine atom number.
• Similar viscosity and Li+ mobilities were observed in ethyl-2,2,2-trifluoroethyl carbonate (ETFEC) and di-1,1,2,2,2-pentafluoroethyl carbonate (DTFEC) solutions.
• Electric fields induce solvent molecule ordering, decreasing dielectric constants and potentially reducing ion mobility.

Conclusions:

• Electrolyte dynamic properties are largely independent of fluorine content in these carbonates under free conditions.
• Electric fields significantly alter solvent structure, impacting ion pair formation and charge-discharge rates.
• Findings offer insights into optimizing fluorinated carbonate electrolytes for high-voltage battery applications.