A Study on Corrosion of Al-Clad Coin Cell Cases in High-Voltage Li-Ion Battery

Aluminum-coated (Al-Clad) coin cell case has long been introduced to evaluate high-voltage cathode materials and electrolytes in battery research. However, our study on graphite/LiNi0.80Co0.10Mn0.10O2 (Gr/NCM811) coin cells indicates that the Al-Clad case resulted in even worse performance than the pristine stainless steel (SS) case. Post-mortem observation finds that the Al-Clad case was severely corroded, while the SS case seems to remain intact. To understand this unusual phenomenon, the corrosion behavior of the Al-Clad cases in LiPF6 electrolyte and lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte, respectively, is studied. It is shown that the coating of Al on the Al-Clad cases is not dense, allowing liquid electrolytes to permeate through and contact the underlying SS core case, forming galvanic cells between the Al coating and the SS core case. At high potentials, the galvanic cells reduce the over-potential of Al oxidation, promoting corrosion of the Al coating. As such, the Al coating does not protect the underlying SS core case, oppositely, making the corrosion of itself more severe. The results of this work reveal that to support high-voltage applications, the coating of Al on the Al-Clad cases must be dense, otherwise, it makes the corrosion worse.