Assessing the Oxidation Behavior of EC:DMC Based Electrolyte on Non-Catalytically Active Surface

The race for developing Li-ion batteries positive electrodes with always greater energy density has recently renewed interest towards understanding the formation of the so-called cathode electrolyte interface (CEI) forming upon cycling at high potential. In this work, we used an approach combining electrochemical measurements with physical characterizations to study the different anodic events occurring for the state-of-the-art EC:DMC 1M LiPF6 (LP30) electrolyte. Doing so, we could find that EC-related species are first oxidized before the oxidation of DMC-related species at greater potential which forms a film relatively rich in organic polycarbonates species. Using a soluble redox probe, we could then demonstrate that while this organic layer is partially passivating, it is unstable with time and cycling. In fact, only reaching a potential as high as 5.4 V vs Li+/Li for several hours leads to the formation of a perfectly stable and passivating CEI. (C) 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.