Influence of LiPF₆on the Aluminum Current Collector Dissolution in High Voltage Lithium Ion Batteries after Long-Term Charge/Discharge Experiments

The long-term influence of the most commonly used conducting salt in electrolyte formulations, lithium hexafluorophosphate, on the aluminum current collector stability in high voltage lithium ion batteries was investigated. By means of different surface sensitive techniques (scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy), after 1003 simulated charge/discharge cycles, anodic aluminum dissolution was found to take place at elevated potential (4.95 V vs. Li/Li + ) but only to a minor extent. Pitting of the Al collector could be assessed in the nanometer range. Furthermore, it could be revealed that local pit formation is related to local "native" grooves on the aluminum foil, which develop during the production process of the aluminum foil. The obtained results were evaluated and compared to a reference electrolyte containing the alternative conducting salt lithium bis(trifluoromethanesulfonyl)imide. Our findings imply two possible mechanisms for the occurring Al dissolution behavior at elevated potentials. Either, an accelerated aluminum dissolution process, or a continuous passivation/LiPF 6 -decomposition process.