Conventional Electrolyte and Inactive Electrode Materials in Lithium‐Ion Batteries: Determining Cumulative Impact of Oxidative Decomposition at High Voltage

• Published in: ChemSusChem Vol. 13; no. 19; pp. 5301 - 5307
• Main Authors: Streipert, Benjamin, Stolz, Lukas, Homann, Gerrit, Janßen, Pia, Cekic‐Laskovic, Isidora, Winter, Martin, Kasnatscheew, Johannes
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 07.10.2020; John Wiley and Sons Inc
• Subjects: batteries; Decomposition; Discharge; Electrode materials; Electrodes; electrolyte oxidation; high voltage; inactive materials; lithium; Lithium-ion batteries; Oxidation; Stability; lithium; electrolyte oxidation; high voltage; inactive materials; batteries
• DOI: 10.1002/cssc.202001530
• ISSN: 1864-5631

High‐voltage electrodes based on, for example, LiNi0.5Mn1.504 (LNMO) active material require oxidative stability of inactive materials up to 4.95 V vs. Li|Li+. Referring to literature, they are frequently supposed to be unstable, though conclusions are still controversial and clearly depend on the used investigation method. For example, the galvanostatic method, as a common method in battery research, points to the opposite, thus to a stability of the inactive materials, which can be derived from, for example, the high decomposition plateau at 5.56 V vs. Li|Li+ and stable performance of the LNMO charge/discharge cycling. This work aims to unravel this apparent contradiction of the galvanostatic method with the literature by a thorough investigation of possible trace oxidation reactions in cumulative manner, that is, over many charge/discharge cycles. Indeed, the cumulated irreversible specific capacity amounts to ≈10 mAh g−1 during the initial 50 charge/discharge cycles, which is determined by imitating extreme LNMO high‐voltage conditions using electrodes solely consisting of inactive materials. This can explain the ambiguities in stability interpretations of the galvanostatic method and the literature, as the respective irreversible specific capacity is obviously too low for distinct detection in conventional galvanostatic approaches and can be only detected at extreme high‐voltage conditions. In this regard, the technique of chronoamperometry is shown to be an effective and proper complementary tool for electrochemical stability research in a qualitative and quantitative manner. Step by step: Electrochemical stability of, for example, electrolytes is still debated. Depending on the method, different oxidation onsets are reported. In contrast, battery application demonstrates stability even up to 5.56 V vs. Li|Li+. This apparent contradiction is investigated in this work. It could be shown, that the oxidation reactions proceed only in traces, thus can only be detected in cumulative manner during galvanostatic battery operation and/or chronoampeometric techniques.