The stability of oxidized shuttle molecules in electrolyte and in contact with the electrode materials is a critical issue in the search for redox shuttle additives for Li-ion cells. In this paper, it is argued that the stability cannot be estimated efficiently by calculating the rate constants for reactions between oxidized shuttle molecules and the complex "reaction cocktail" that the electrolyte and electrodes present. Instead, a realistic, alternate approach to estimating shuttle stability has been found. The binding energy, E-b(ER), between oxidized shuttle molecules and an ethyl radical, ER, is used to estimate the relative reactivity of oxidized shuttle molecules. The calculated binding energies, E-b(ER), of 19 selected oxidized shuttle molecules show approximately the correct trend with respect to their experimental stability. E-b(ER) is used as a tool to explain the stability of various stable shuttle molecules. Now, both the oxidation potential and the stability of candidate shuttle molecules can be predicted. This is speeding up the search for stable shuttle molecules with the desired redox potential. (c) 2006 The Electrochemical Society.