title: Evidence for lithium superoxide-like species in the discharge product of a Li-O2 battery.
abstract: 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.
authors: Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL, USA.
authors: Junbing
authors: J
authors: Yang
authors: Dengyun
authors: D
authors: Zhai
authors: Hsien-Hau
authors: HH
authors: Wang
authors: Kah Chun
authors: KC
authors: Lau
authors: John A
authors: JA
authors: Schlueter
authors: Peng
authors: P
authors: Du
authors: Deborah J
authors: DJ
authors: Myers
authors: Yang-Kook
authors: YK
authors: Sun
authors: Larry A
authors: LA
authors: Curtiss
authors: Khalil
authors: K
authors: Amine