Determining oxidative stability of battery electrolytes: validity of common electrochemical stability window (ESW) data and alternative strategies

Increasing the operation voltage of electrochemical energy storage devices is a viable measure to realize higher specific energies and energy densities. A sufficient oxidative stability of electrolytes is the predominant requirement for successful high voltage applicability. The common method to investigate oxidative stability of LIB electrolytes is related to determination of the electrochemical stability window (ESW), on e.g. Pt or LiMn2O4 electrodes. However, the transferability of the obtained results to practical systems is questionable for several reasons. In this work, we evaluated the validity of the potentiodynamic based ESW method by comparing the obtained data with the results of galvanostatic based techniques, applied on commercial positive electrodes. We demonstrated that the oxidative stabilities, determined by the two techniques, are in good accordance with each other. However, the investigation of electrolytes being incompatible to Li metal, renders conventional ESW measurements useless when metallic Li is used as counter - and reference electrode in the ESW setup. For this reason, we introduced an alternative setup based on Li4Ti5O12 full cells. On the example of a butyronitrile-based electrolyte, we finally demonstrated that this electrolyte is not only reductively but also oxidatively less stable than common LiPF6/organic carbonate based electrolytes.