Exploring the Impact of In Situ-Formed Solid-Electrolyte Interphase on the Cycling Performance of Aluminum Metal Anodes

Unwanted processes in metal anode batteries, e.g., non-uniform metal electrodeposition, electrolyte decomposition, and/or short-circuiting, are not fully captured by the electrolyte bulk solvation structure but rather defined by the electrode-electrolyte interface and its changes induced by cycling conditions. Specifically, for aluminum-ion batteries (AIBs), the role of the solid-electrolyte interphase (SEI) on the Al⁰ electrodeposition mechanism and associated changes during resting or cycling remain unclear. Here, we investigated the current-dependent changes at the electrified aluminum anode/ionic liquid electrolyte interface to reveal the conditions of the SEI formation leading to irreversible cycling in the AIBs. We identified that the mechanism of anode failure depends on the nature of the counter electrode, where the areal capacity and cycling current for Al⁰ electrodeposition dictates the number of successful cycles. Notwithstanding the differences behind unstable aluminum anode cycling in symmetrical cells and AIBs, the uniform removal of electrochemically inactive SEI components, e.g., oxide-rich or solvent-derived organic-rich interphases, leads to more efficient cycling behavior. These understandings raise the importance of using specific conditioning protocols for efficient cycling of the aluminum anode in conjugation with different cathode materials.