Sigma-Holes in Battery Materials Using Iso-Electrostatic Potential Surfaces

Cristhian Roman-Vicharra,Diego Galvez-Aranda,Jorge Seminario,Franz Franco-Gallo,Ryan Alaminsky,Perla Balbuena

doi:10.3390/cryst8010033

Cristhian Roman-Vicharra, Diego Galvez-Aranda + Show 4 more

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https://doi.org/10.3390/cryst8010033

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Journal: Crystals	Publication Date: Jan 12, 2018
Citations: 6	License type: CC BY 4.0

Affiliation: Texas A&M University

Abstract

The presence of highly electronegative atoms in Li-ion batteries anticipates the formation of σ-hole regions that may strongly affect the ionic conductivity. The σ-hole consists of a region of positive electrostatic potential extending in the direction of the covalent bond between atoms of groups IV–VII due to anisotropic charge distribution. Graphite electrodes in Li-ion batteries that become halogenated due to the electrolyte, as well as some solid electrolyte materials, can exhibit these σ-holes. Since Li-ions should be able to drift in any part of the battery, the fact that they can be attracted and eventually absorbed by regions of strong negative potentials produced by high-electronegativity counterions becomes detrimental to ionic conductivity. Therefore, the presence of positive well-defined regions, repulsive to the Li-ions, might act as lubricant for Li-ions drifting through electrolytes, thus improving the Li-ion conductivity. In addition, the σ-holes might also have a strong effect on the formation of the passivating layer, known as the solid electrolyte interphase (SEI) at electrode surfaces, which is of paramount importance for the performance of rechargeable batteries. Here we investigate the existence of σ-holes on surfaces of graphite anodes and of a few solid electrolytes by examining the electrostatic potentials calculated using density functional theory.

Highlights

IntroductionGraphite electrodes in Li-ion batteries that become halogenated due to the electrolyte, as well as some solid electrolyte materials, can exhibit these σ-holes
We can see the new approach can be used to show the domains at which the σ-hole is active in halogenated compounds, which the Molecular electrostatic potentials (MEPs) spectrum tends to miss by illustrating the potential on isodensities
Successful demonstration of the σ-hole in molecules allows a larger-scale study by taking advantage of periodic boundary conditions of first-principle programs, such as Vienna ab initio simulation package (VASP), when advantage of periodic boundary conditions of first-principle programs, such as VASP, when examining examining isopotentials in crystal surfaces

Summary

Introduction

Graphite electrodes in Li-ion batteries that become halogenated due to the electrolyte, as well as some solid electrolyte materials, can exhibit these σ-holes. 1. Introduction σ-holes are particular electronic arrangements where a region of positive electrostatic potential extends in the direction of the covalent bond between atoms of groups IV–VII due to anisotropic charge distribution. Graphite electrodes in Li-ion batteries that become halogenated due to electrolyte decomposition, as well as of some solid electrolyte materials, can exhibit these σ-holes. The importance of these electronic distributions is that they can favor ionic or electronic motion in directions that would not be possible in their absence.

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