PubAg

Main content area

Lithium Peroxide Surfaces Are Metallic, While Lithium Oxide Surfaces Are Not

Author:
Radin, Maxwell D., Rodriguez, Jill F., Tian, Feng, Siegel, Donald J.
Source:
Journal of the American Chemical Society 2012 v.134 no.2 pp. 1093-1103
ISSN:
1520-5126
Subject:
batteries, crystallites, electrochemistry, electron transfer, lithium, methodology, oxygen, thermodynamics
Abstract:
The thermodynamic stability and electronic structure of 40 surfaces of lithium peroxide (Li₂O₂) and lithium oxide (Li₂O) were characterized using first-principles calculations. As these compounds constitute potential discharge products in Li–oxygen batteries, their surface properties are expected to play a key role in understanding electrochemical behavior in these systems. Stable surfaces were identified by comparing 23 distinct Li₂O₂ surfaces and 17 unique Li₂O surfaces; crystallite areal fractions were determined through application of the Wulff construction. Accounting for the oxygen overbinding error in density functional theory results in the identification of several new Li₂O₂ oxygen-rich {0001} and {11̅00} terminations that are more stable than those previously reported. Although oxygen-rich facets predominate in Li₂O₂, in Li₂O stoichiometric surfaces are preferred, consistent with prior studies. Surprisingly, surface-state analyses reveal that the stable surfaces of Li₂O₂ are half-metallic, despite the fact that Li₂O₂ is a bulk insulator. Surface oxygens in these facets are ferromagnetic with magnetic moments ranging from 0.2 to 0.5 μB. In contrast, the stable surfaces of Li₂O are insulating and nonmagnetic. The distinct surface properties of these compounds may explain observations of electrochemical reversibility for systems in which Li₂O₂ is the discharge product and the irreversibility of systems that discharge to Li₂O. Moreover, the presence of conductive surface pathways in Li₂O₂ could offset capacity limitations expected to arise from limited electron transport through the bulk.
Agid:
5385385