Electrochemical potential window of battery electrolytes: The HOMO-LUMO misconception

Pekka Peljo*, Hubert H. Girault

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

106 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)2306-2309
Number of pages4
JournalEnergy and Environmental Science
Issue number9
Publication statusPublished - 1 Sep 2018
MoE publication typeA1 Journal article-refereed


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