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Lithium–Oxygen Cells: An Analytical Model to Explain Key Features in the Discharge Voltage Profiles
Author(s) -
Rinaldi Ali,
Wijaya Olivia,
Hoster Harry
Publication year - 2016
Publication title -
chemelectrochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.182
H-Index - 59
ISSN - 2196-0216
DOI - 10.1002/celc.201600184
Subject(s) - overpotential , tafel equation , voltage , lithium (medication) , chemistry , electrochemistry , analytical chemistry (journal) , electrode , superoxide , materials science , electrical engineering , chromatography , medicine , biochemistry , endocrinology , enzyme , engineering
Lithium–oxygen (Li–O 2 ) cells are popular because of their potentially high energy density. A characteristic fingerprint of a given cell is the voltage profile during constant‐current discharge. We suggest that the typical initial dip and the following increase of the voltage result from a temporary increase and slow decrease in the concentration of dissolved superoxide, respectively, feeding into the Nernst equation. The steady‐state superoxide concentration decreases as the surface area of the solid precipitation product (Li 2 O 2 ) increases. Importantly, these products bury the electrochemically active carbon surface. Assuming that the electrochemical step only occurs on bare carbon, the Tafel equation provides an expression for the increasing overpotential as a result of the shrinking effective electrode area. This boils the discharge voltage profile down to the sum of two logarithms, grasping all relevant features in the recorded discharge voltage profiles.