The performance of Li-ion batteries (LIB) are 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 remains “the most important but the least understood in LIB”. Simulations can provide critical insights to the electrochemical reactions at the electrode/SEI/electrolyte interface. To overcome the simulation size limitation of Density Function Theory (DFT).and the lack of electrochemistry description of ReaxFF, Density Functional Tight Binding (DFTB) was used to model the charge transfer reaction at a Li/Li2CO3/liquid Ethylene carbonate (EC) electrolyte interface. In this study, we first developed a new set of DFTB parameters for Li-X (X=Li, H, C, O) interactions by fitting and calibrating with various DFT calculations. Then, the lithiation and delithiation process was simulated. The simulation clearly shows 4 layers Li2CO3 can effectively protect the Li electrode surface. During de-lithiation, it is energetically favorable to form a void at the Li/Li2CO3 interface. 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 reaction, electron is always located on the Li-metal slab, if the Li2CO3 layer is thick enough, corresponding to the applied electron density or voltage. The energy profile of this reaction was simulated under different voltage. The impact of intrinsic point defects (as Li+ interstitials) in Li2CO3 on the charge transfer reaction barrier is also investigated.

Computational insights to charge transfer reactions at the complex electrode/SEI/electrolyte interface

254th National Meeting (2017)

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