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Issue 9, 2018
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Electrochemical potential window of battery electrolytes: the HOMO–LUMO misconception

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Abstract

A widespread misconception in the lithium ion battery literature is the equality of the energy difference of HOMO and LUMO of the solvent with the electrochemical stability window. HOMO and LUMO are concepts derived from approximated electronic structure theory while investigating electronic properties of isolated molecules, and their energy levels do not indicate species participating in redox reactions. On the other hand, redox potentials are directly related to the Gibbs free energy difference of the reactants and products. While redox potentials in some cases show strong correlation with HOMO energies, the offset can be of several eVs. Presence of electrolytes and other molecules can also significantly affect the redox potentials of the solvent leading to offset as high as 4 eV from the HOMO energies. In this opinion we provide a correct thermodynamic representation for the electrochemical stability of the electrolyte, based on redox potentials and Fermi level of the electron in solution, and demonstrate that the use of terms HOMO and LUMO should be avoided when talking about the electrochemical stability of electrolytes. Instead, it is more correct to speak of potential of electrolyte reduction at negative potentials, and of potential of solvent oxidation at positive potentials.

Graphical abstract: Electrochemical potential window of battery electrolytes: the HOMO–LUMO misconception

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Publication details

The article was received on 02 May 2018, accepted on 27 Jul 2018 and first published on 28 Jul 2018


Article type: Opinion
DOI: 10.1039/C8EE01286E
Citation: Energy Environ. Sci., 2018,11, 2306-2309
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    Electrochemical potential window of battery electrolytes: the HOMO–LUMO misconception

    P. Peljo and H. H. Girault, Energy Environ. Sci., 2018, 11, 2306
    DOI: 10.1039/C8EE01286E

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