The performance of Li-ion batteries (LIB) ar highly dependent on the electrochemical reactions occurring at the Solid Electrolyte Interface (SEI). However, its nanometric scale thickness combined with its complex structure makes the SEI remain “the most important but the least understood in LIB”. Simulations can provide critical insights to the electrochemical reactions at the electrode/SEI/electrolyte interface. However, due to the simulation size limitation of Density Function Theory (DFT), it is very challenging to predict the ionic transport in the multicompoent SEI layer and at the electrode/SEI/electrolyte complex interface. In this talk, we introduce two simualtion approaches to overcome this limit. To model the charge transfer reaction at a Li/Li2CO3/liquid electrolyte interface, we employed Density Functional Tight Binding (DFTB) method with newly parameterized Li-X (X=Li, H, C, O) interactions. The simulation clearly shows during delithiation, it is energetically favorable to remove Li atoms at the Li/Li2CO3 interface than from the bulk of Li. The lithiation process was simulated as three steps: Li+ desolvation at the SEI/Electrolyte interface, Li+ diffusion through the Li2CO3 layer, and annihilation of e- and Li+ at the Li surface. During this charge transfer step, electron is always located on the Li-metal slab corresponding to the applied electron density or voltage. The energy profile of this reaction was simulated under different voltage. It was found at the experimetnally defiend zero voltage of Li+/Li0, the metallic lithiu surface is already negatively charged. It impact on Li plating and stripping will be discussed. To capture the multi-component nature of SEI, we developed a (DFT) informed space charge model for the design of an artificial SEI consisting of lithium fluoride (LiF) and lithium carbonate (Li2CO3). Specifically, we found that, in the ionic space charge region of Li2CO3 near the LiF/Li2CO3 interface, Li ion interstitial is accumulated but the electron is depleted. This led to an engineered nanocomposite LiF and Li2CO3 as an artificial SEI, in which the ionic conduction can be enhanced and the electron leakage through the SEI can be reduced.

Simulation of lithium ion transport through the complex electrode/SEI/electrolyte interface

255th National Meeting (2018)

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