A solid electrolyte interphase is formed when electrolyte components are reduced during the cycling of lithium and sodium ion batteries. The SEI formed impacts battery lifetime and efficiency.  Typically, the electrolyte solutions are a complex mixture of organic carbonates. Recently, efforts have been made to engineer battery electrolytes to extend the cycling life of lithium and sodium ion batteries.  It is still unclear why these additives are effective at extending the cycling life of the batteries.  In this work, we use the vibrational probe, methyl thiocyanate (MeSCN), in 2D IR spectroscopy experiments to study the local solvent dynamics in individual electrolyte constituents and a full electrolyte cocktail.  The base electrolyte cocktail contains ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a 1:1:1 ratio.  The addition of 5% fluoroethylene carbonate (FEC) and the subsequent addition of sodium perchlorate (NaClO<sub>4</sub>) as the supporting electrolyte, significantly changes the local solvent dynamics of the cocktail. In addition, the spatial dependence of the chemical dynamics present in these solutions is explored using <i>in situ</i> 2D IR imaging experiments.  These results provide insight to the chemical dynamics at play in the formation of the SEI in a model electrode-electrolyte architecture.

Exploring the spatial dependence of chemical dynamics under a voltage bias using 2D IR imaging

2019 Fall National Meeting

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