Transferable Self-Consistent Charge Density Functional Tight-Binding Parameters for Li–Metal and Li-Ions in Inorganic Compounds and Organic Solvents

Abstract

When a Li–metal electrode immerses in the electrolytes containing organic solvents, it is always covered by a thin layer of solid electrolyte interphase (SEI) containing both inorganic and organic compounds. While simulating the electrochemical reactions occurring at this interface is essential to understand electrolyte decomposition and Li dendrite formation that impact the life and safety of Li-ion batteries, conventional density functional theory (DFT) or force field methods are either limited by size or by accuracy. Therefore, the self-consistent-charge density functional tight-binding (SCC-DFTB) approach was taken in this research. We first developed a parametrization scheme for mixed valence lithium (Li0 and Li+) within the SCC-DFTB framework and then developed a new set of parameters for Li–X (X = Li, H, O, and C) interactions. The newly developed parameters were validated through comparison with DFT predictions for a range of materials, including Li, Li2O, and Li2CO3, and Li+ ions dissolved in ethylene carbonate (EC) solvent. The SCC-DFTB calculated properties, including electric, structural, surface, and interface properties, and Li+ solvation energy and diffusion coefficient in liquid EC agreed well with DFT results. The effect of SEI thickness in blocking electron transfer and preventing electrolyte reduction was captured by a Li/Li2CO3/liquid-EC interface model. The newly developed SCC-DFTB parameters provide a reliable and transferable method to simulate charge transfer reactions at the complex Li–metal/SEI/electrolyte for Li-ion batteries.