Electronic Structure of Lithium Peroxide Clusters and Relevance to Lithium鈥揂ir Batteries

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• 作者：Kah Chun Lau ; Rajeev S. Assary ; Paul Redfern ; Jeffrey Greeley ; Larry A. Curtiss
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：November 15, 2012
• 年：2012
• 卷：116
• 期：45
• 页码：23890-23896
• 全文大小：424K
• 年卷期：v.116,no.45(November 15, 2012)
• ISSN：1932-7455

文摘

The prospect of Li鈥揳ir(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鈥揙 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鈥揳ir batteries including electronic conductivity and charge overpotentials.