Publication
Increasing the upper cut‐off potential of NMC811 electrodes beyond 4.3 V versus Li/Li+ offers the potential to increase the specific energy of lithium‐ion battery cells by 20%. However, high‐voltage operation typically leads to accelerated aging resulting from a combination of degradation phenomena that are difficult to deconvolute. This study focuses on isolating the impact of electrolyte salt decomposition by replacing the unstable lithium hexafluorophosphate (LiPF6) salt, which acts as a source of fluorine ions in the electrolyte, with the more stable lithium bis(trifluoromethane)sulfonimide (LiTFSI) salt. However, in the absence of fluorine ions, anodic dissolution of the aluminum current collector becomes a major issue, causing cell failure after only a few cycles. Tantalum current collectors show robustness against anodic dissolution without fluorine ion passivation even at high cell voltage, enabling the studies of lithium‐ion batteries in fluorine‐free conditions. Both NMC811||LTO and NMC811||graphite cells exhibit superior cycling stability at high voltage and/or elevated temperature with LiTFSI electrolyte due to reduced transition metal dissolution without the need for fluorine scavenging additives. Tantalum current collectors also enable the study of other high‐voltage cell chemistries in the absence of fluorine ions, providing precious new insights into the aging phenomena of next‐generation high‐energy batteries.