Electronic Structure of Lithium Peroxide Clusters and Relevance to Lithium–Air Batteries

• Published in: Journal of physical chemistry. C Vol. 116; no. 45; pp. 23890 - 23896
• Main Authors: Lau, Kah Chun, Assary, Rajeev S, Redfern, Paul, Greeley, Jeffrey, Curtiss, Larry A
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 15.11.2012
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic structure of nanoscale materials : clusters, nanoparticles, nanotubes, and nanocrystals; Exact sciences and technology; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Physics; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Trimer; Electronic properties; Electrical conductivity; Energy levels; Electronic conductivity; Particle cluster; High density; Singlet state; Bond lengths; Monomers; Surface structure; Lithium battery; Triplet state; Electronic structure; High spin states; Morphology; Tetramer; Electrochemistry; Density functional method; Dimers; Microstructure; Nanomaterial synthesis
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp306024f

The prospect of Li–air(oxygen) batteries has generated much interest because of the possibility of extending the range of electric vehicles due to their potentially high gravimetric density. The exact morphology of the lithium peroxide formed during discharge has not been determined yet, but the growth likely involves nanoparticles and possibly agglomerates of nanoparticles. In this article, we report on density functional calculations of stoichiometric lithium peroxide clusters that provide evidence for the stabilization of high spin states relative to the closed shell state in the clusters. The density functional calculations indicate that a triplet state is favored over a closed shell singlet state for a dimer, trimer, and tetramer of lithium peroxide, whereas in the lithium peroxide monomer, the closed shell singlet is strongly favored. Density functional calculations on a much larger cluster, (Li2O2)16, also indicate that it similarly has a high spin state with four unpaired electrons located on the surface. These results have been confirmed by higher level G4 theory calculations that indicate that the singlet and triplet states of the dimer are nearly equal in energy and that the triplet state is more stable than the singlet for clusters larger than the dimer. The high spin states of the clusters are characterized by O–O moieties protruding from the surface, which have superoxide-like characteristics in terms of bond distances and spin. The existence of these superoxide-like surface structures on stoichiometric lithium peroxide clusters may have implications for the electrochemistry of formation and decomposition of lithium peroxide in Li–air batteries including electronic conductivity and charge overpotentials.