Here, HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) are marked. During the reduction, an electron is added to the electrolyte's LUMO, while removing an electron from its HOMO results in oxidation. It is beneficial for the Fermi level of the positive electrode to be higher than the electrolyte's HOMO. This would imply that there will be no electron transfer between the electrolyte and positive electrode and that it will not oxidize.