Electron Leakage through Extended Defects in Inorganic Solid Electrolyte Interphase -- a Non-Equilibrium Green's Function/Density Functional Theory Study

Abstract

The solid-electrolyte interphase (SEI) that forms on lithium ion battery (LIB) anodes prevents the leakage of electrons to the electrolyte, which causes electrolyte degradation and capacity fade. Grain boundaries (GB) between inorganic SEI components, like LiF/LiF or LiF/Li2CO3 boundaries, have been suggested to accelerate Li+ transport[1]. However, SEI GBs on lithium metal anode surfaces have also been predicted to support the existence of Li atoms and nanoclusters at low voltages[2], potentially leading to nucleus for hazardous lithium plating. In this presentation, we further examine the possibility of electron tunneling from the lithium anode through extended defects in LiF films. Using the non-equilibrium Green's function technique (NEGF-DFT), we find that GBs enhance electron tunneling in thin LiF films by 1-2 orders magnitude, depending on the bias. Extrapolating to 5 nm thick films using the WKB method suggests that GBs may enhance electron leakage by up to 9 orders of magnitude. This emphasizes that GBs in the inorganic SEI film are hotspots with respect to electron leakage. We propose that the further development of NEGF algorithms to enable large scale applications to battery interfaces is crucial for predicting SEI passivating properties.[1] J. Pan, Q. Zhang, X. Xiao, Y. Cheng, and Y. Qi, Design of Nanostructured Heterogeneous Solid Ionic Coatings through a Multiscale Defect Model, ACS Appl. Mater. Interfaces 8, 5687 (2016).[2] K. Leung and K. L. Jungjohann, Spatial Heterogeneities and Onset of Passivation Breakdown at Lithium Anode Interfaces, J. Phys. Chem. C 121, 20188 (2017).Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the document do not necessarily represent the views of the U.S. Department of Energy or the United States Government. Figure 1