SEI Growth on Aluminum-Metal Anodes in Aluminum Dual-Ion Batteries
Authors: Kieser Joy , Aktekin Burak , Rohnke Marcus , Janek Jürgen 
Published: December 2024

The commercialization of sodium-ion batteries can be regarded as the first step towards diversification of rechargeable batteries beyond the lithium-ion technology. Especially multivalent metals are becoming more and more attractive due to the growing demand for alternative rechargeable batteries and sustainability. For specific applications, aluminum dual-ion batteries are regarded as promising alternatives to lithium and sodium-ion batteries.

An aluminum graphite dual-ion cell can be constructed from a chloroaluminate room-temperature ionic liquid, aluminum foil, and graphite.[1] As raw materials, aluminum and graphite are inexpensive and readily available, making these secondary aluminum batteries attractive for stationary energy storage. In the aluminum graphite dual-ion battery, AlCl4
− is reversibly intercalated into the graphite structure, while aluminum is reversibly deposited and dissolved on the negative electrode.[2] The electrochemical performance of typical laboratory-type cells is limited by the cathode active material performance as the electrolyte is used in significant excess in such cells.[3] With these experimental conditions, the electrolyte consumption for side reactions, such as forming a solid electrolyte interphase (SEI), is overlooked. The same applies to using aluminum foil as the negative electrode, where excess aluminum can conceal the negative impact of side reactions. Studies so far have only addressed the formation of an unstable SEI between aluminum metal and electrolyte, and the instability of the native oxide layer.[4] However, the presence of the oxide layer makes it challenging to observe interface development and parasitic side reactions of freshly electrodeposited metal.

In this study, we employed an electrochemical coulometric titration technique to quantify the consumption of electrodeposited aluminum by parasitic side reactions in 1-ethyl-3-methylimidazolium chloride-aluminum chloride ionic liquids. We were able to quantify side reactions using coulometric titration time analysis (CTTA)[5], considering only the interactions between the electrodeposited metal and the electrolyte. We found a linear dependency on the square root of time for the charge consumption. This shows that SEI formation on electrodeposited aluminum follows the kinetics of diffusion limited growth. Complementary surface analysis is in progress to verify the existence of an SEI and elucidate its chemical composition. A deeper understanding of SEI formation and stability on aluminum metal anodes will undoubtedly benefit the development of more efficient aluminum dual-ion batteries.

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