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The influence of anisotropic surface stresses and bulk stresses on defect thermodynamics in LiCoO2 nanoparticles

Stein, Peter and Moradabadi, Ashkan and Diehm, P. Manuel and Xu, Bai-Xiang and Albe, Karsten (2018):
The influence of anisotropic surface stresses and bulk stresses on defect thermodynamics in LiCoO2 nanoparticles.
In: Acta Materialia, pp. 225-240, 159, ISSN 13596454, DOI: 10.1016/j.actamat.2018.07.046, [Article]

Abstract

The demand for higher specific capacity and rate capability has led to the adoption of nanostructured electrodes for lithium-ion batteries. At these length scales, surface effects gain an appreciable impact not only on the electrochemical and mechanical behavior of the electrode material, but also on defect thermodynamics. The focus of this study is the distribution of surface-induced bulk stresses in a LiCoO2 nanoparticle and their impact on the migration of Li vacancies. LiCoO2 is a prototypical cathode material, where the diffusion of Li is mediated by the vacancy mechanism.

For this investigation, elastic parameters and anisotropic surface stress components are computed using Density Functional Theory calculations. They are incorporated into a surface-enhanced continuum model, implemented by means of the Finite Element method. The particle geometry is derived from a Wulff construction, and changes in the formation energy and migration barriers of a Li vacancy are determined using the defect dipole tensor concept.

Within the considered nanoparticle, the surface stresses result in a highly heterogeneous bulk stress distribution with a vortex-like transition region between the tensile particle core and its non-uniformly stressed boundaries. Both the center and the exterior of the particle show enhanced formation energy and migration barriers for of a Li vacancy. These experience a reduction in the transition region in the particle, culminating in a peak increase in vacancy diffusivity and ionic conductivity by circa 10% each. For a particle at a length-scale of 10 nm, this yields an overall increase in ionic conductivity by a mere 0.8%. This surface stress-enhanced conductivity decays rapidly with increasing particle size. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Item Type: Article
Erschienen: 2018
Creators: Stein, Peter and Moradabadi, Ashkan and Diehm, P. Manuel and Xu, Bai-Xiang and Albe, Karsten
Title: The influence of anisotropic surface stresses and bulk stresses on defect thermodynamics in LiCoO2 nanoparticles
Language: English
Abstract:

The demand for higher specific capacity and rate capability has led to the adoption of nanostructured electrodes for lithium-ion batteries. At these length scales, surface effects gain an appreciable impact not only on the electrochemical and mechanical behavior of the electrode material, but also on defect thermodynamics. The focus of this study is the distribution of surface-induced bulk stresses in a LiCoO2 nanoparticle and their impact on the migration of Li vacancies. LiCoO2 is a prototypical cathode material, where the diffusion of Li is mediated by the vacancy mechanism.

For this investigation, elastic parameters and anisotropic surface stress components are computed using Density Functional Theory calculations. They are incorporated into a surface-enhanced continuum model, implemented by means of the Finite Element method. The particle geometry is derived from a Wulff construction, and changes in the formation energy and migration barriers of a Li vacancy are determined using the defect dipole tensor concept.

Within the considered nanoparticle, the surface stresses result in a highly heterogeneous bulk stress distribution with a vortex-like transition region between the tensile particle core and its non-uniformly stressed boundaries. Both the center and the exterior of the particle show enhanced formation energy and migration barriers for of a Li vacancy. These experience a reduction in the transition region in the particle, culminating in a peak increase in vacancy diffusivity and ionic conductivity by circa 10% each. For a particle at a length-scale of 10 nm, this yields an overall increase in ionic conductivity by a mere 0.8%. This surface stress-enhanced conductivity decays rapidly with increasing particle size. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Journal or Publication Title: Acta Materialia
Volume: 159
Uncontrolled Keywords: Anisotropic surface stress, Nanoparticle, Defect thermodynamics, Defect dipole tensor, Lithium cobalt oxide
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Mechanics of functional Materials
11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
Zentrale Einrichtungen
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ)
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ) > Hochleistungsrechner
Date Deposited: 19 Jul 2018 13:32
DOI: 10.1016/j.actamat.2018.07.046
Funders: German Research Foundation DFG, Grant Number STE 2350/1-1, Adolf Messer Foundation
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