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Evidence for lithium superoxide-like species in the discharge product of a Li–O2 battery

2013; Royal Society of Chemistry; Volume: 15; Issue: 11 Linguagem: Inglês

10.1039/c3cp00069a

1463-9084

Junbing Yang, Qiang Cai, Hsien-Hau Wang, Kah Chun Lau, John A. Schlueter, Peng Du, Deborah J. Myers, Yang‐Kook Sun, Larry A. Curtiss, Khalil Amine,

Advanced Battery Technologies Research

We report on the use of a petroleum coke-based activated carbon (AC) with very high surface area for a Li-O(2) battery cathode without the use of any additional metal catalysts. Electrochemical measurement in a tetra(ethylene) glycol dimethyl ether-lithium triflate (TEGDME-LiCF(3)SO(3)) electrolyte results in two voltage plateaus during charging at 3.2-3.5 and 4.2-4.3 V versus Li(+)/Li. Herein we present evidence from Raman and magnetic measurements that the lower plateau corresponds to a form of lithium peroxide with superoxide-like properties characterized by a low temperature magnetic phase transition and a high O-O stretching frequency (1125 cm(-1)). The magnetic phase transition and the high O-O stretching frequency disappear when charged to above 3.7 V. Theoretical calculations indicate that a surface superoxide structure on lithium peroxide clusters and some lithium peroxide surfaces have an unpaired electron and a high O-O stretching frequency that help explain the observations. These results provide evidence that the form of the lithium peroxide discharge product is important to obtaining a low charge overpotential, and thus improving the round-trip efficiency between discharge and charge.