Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 15, Issue 11, Pages 3764-3771Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c3cp00069a
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Funding
- U.S. Department of Energy Office of Basic Energy Science-Division of Materials Science [DE-AC02-06CH11357]
- Human Resources Development of the Korea Institute of Energy Technology Evaluation of Planning (KETEP)
- Korea government of Ministry of Knowledge Economy [20114010203150]
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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-LiCF3SO3) 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.
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