Li+-solvent interactions in ternary EC-DEC-TMP electrolyte mixtures by NMR measurements

Abstract

The great importance of Li-ion mobility and the electrode-electrolyte interface interactions for ensuring good performance and high reliability in Li-ion batteries has inspired, in the past few years, the development of a wide range of electrolyte formulations. Accordingly, probing the electrolyte solution structures is now considered pivotal to extend the performance limit of the current Li-ion batteries. However, comprehension of solution structure and ion transport behavior in Li-ion batteries is far from being fully understood. For the above reasons, the development of improved analytical techniques is highly required and NMR is one of the most promising analysis tool in this field. Herein, we report a NMR investigation of the structure and properties of LiPF6-salt solutions based on ternary (ethylene carbonate (EC), diethyl carbonate (DEC) and trimethylphosphate (TMP)) electrolyte solvent mixtures for lithium-ion battery applications. The approach consists of the use of the internally referenced diffusion-ordered spectroscopy (DOSY) method. Solvent coordination ratio, cation valence number as well as self-diffusion coefficients have been thus analyzed upon the different (EC+EDC+TMP) electrolyte formulations and compared with electrochemical measurements