The charge transfer reaction is the fundamental reaction for rechargeable batteries. The energy landscape of this reaction depicts the equilibrium and kinetics of the electrochemical process. Typically, a Li-metal electrode is always covered by a thin layer of solid electrolyte interphase (SEI), forming a complex Li/SEI/electrolyte interface. Predicting the atomic-level process of the electrochemical reaction of Li+ + e- -&gt; Li0 at the complex Li/SEI/electrolyte interface requires requires electronic structure calculations for a large interface structure. We recently developed a new modeling framework to predict the energy landscape of the lithiation/delithiation charge transfer reaction at a Li/Li2CO3/EC-electrolyte interface, with combined density functional theory (DFT) and tight-binding (DFTB) calculations. It was found that Li+ ion is much more energetically favorable to be dissolved in the electrolyte on a zero-charged Li-metal electrode, indicating the SEI is a necessary kinetic barrier to prevent complete solvation of Li-metal into the electrolyte. Due to the large solvation energy of Li+ in the EC-based electrolyte, the Li-metal surface is negatively charged (~0.62 e nm-2) at the experimentally defined zero voltage for Li+/Li0, to maintain the electrochemical equilibrium. The electric field created by the negatively charged surface can reorient the electrolyte into an ordered structure, lower the Li+ ion desolvation energy barrier, and help the Li+ ion transport through the SEI. The charge transfer coefficient, α, in the Butler-Volmer equation was directly computed. Thus, this model enables a bottom-up multiscale modeling approach for ion-transfer electrochemical reactions.

Atomic prediction of energy landscape of the charge transfer reaction at the complex Li/SEI/electrolyte interface

2019 Fall National Meeting

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