(64c) Inhibition and Mechanistic Insights on Electrochemical Corrosion of Aluminum Current Collectors during High-Voltage Battery Operations

Mitigating the corrosion of the cathode current collector, typically aluminum (Al), is critical for high-voltage operation of Li-batteries. It is commonly believed that i) the native Al₂O₃ layer on the Al current collector works as a protective layer to inhibit Al corrosion, suggesting that an increased thickness of Al₂O₃ could be beneficial for corrosion prevention; and ii) fluorinated cathode electrolyte interphase (CEI) formation is helpful for surface passivation of the current collector. In this work, we leverage atomic layer deposition (ALD) to conformally coat the Al current collector with different metal oxide thin films to understand and mitigate the electrochemical corrosion of the Al current collector. We perform both linear sweep voltammetry (LSV) and cyclic voltammetry (CV) on ZnO- and Al₂O₃-modified Al. Surprisingly, the results indicate improved passivation using ZnO-modified Al but increased corrosion from Al₂O₃-modified Al. Hence, rather than corrosion suppression, we find that i) a conformal Al₂O₃ coating increases the corrosion of the Al current collector; and ii) despite a similar extent of fluorination of the CEIs with both ZnO- and Al₂O₃-modified Al current collectors, only the ZnO-modified system results in corrosion passivation.

Mechanistically, nuclear magnetic resonance (NMR) results reveal that bare- and Al₂O₃-modified-Al current collectors accelerate salt degradation in the electrolyte, which is confirmed by the evolution of salt-associated ¹⁹F NMR peaks before and after high voltage potential hold tests. Conversely, the ZnO thin film passivates against high-voltage salt degradation with no changes observed in the salt-associated NMR peaks, an observation that also explains the corrosion protection of the ZnO-modification. Moreover, our constant potential simulation using a solvated jellium method (SJM) also supports the electrochemical corrosion trend where we find low salt adsorption energies for less corrosive ZnO thin films. Importantly, our findings indicate that nanoscale coatings can have impacts beyond the interface, even on bulk electrolyte species.

Lastly, using simple battery architecture, we probe the effect of Al corrosion inhibition on battery cycling performance in different imide-based electrolytes. We find that the ZnO-coated Al current collector facilitates up to a two-and-a-half-fold increase in battery cycle life in recognizably corrosive imide-based electrolytes (1 M LiTFSI/EC-EMC and 1 M LiFSI/DME) with an upper cycling voltage threshold of 4.2 V vs. Li/Li⁺. Our approach enables an understanding of Al corrosion and its impacts on battery cycling performance, revisits the role of native Al₂O₃ in corrosion inhibition, and provides new insights into the origin of corrosion by showing the impact of interfacial coatings on the bulk electrolyte.