Exploring the Impact\nof In Situ-Formed Solid–Electrolyte\nInterphase on the Cycling Performance of Aluminum Metal Anodes

Unwanted processes in metal anode batteries, e.g., non-uniform\nmetal electrodeposition, electrolyte decomposition, and/or short-circuiting,\nare not fully captured by the electrolyte bulk solvation structure\nbut rather defined by the electrode–electrolyte interface and\nits changes induced by cycling conditions. Specifically, for aluminum-ion\nbatteries (AIBs), the role of the solid–electrolyte interphase\n(SEI) on the Al<sup>0</sup> electrodeposition mechanism and associated\nchanges during resting or cycling remain unclear. Here, we investigated\nthe current-dependent changes at the electrified aluminum anode/ionic\nliquid electrolyte interface to reveal the conditions of the SEI formation\nleading to irreversible cycling in the AIBs. We identified that the\nmechanism of anode failure depends on the nature of the counter electrode,\nwhere the areal capacity and cycling current for Al<sup>0</sup> electrodeposition\ndictates the number of successful cycles. Notwithstanding the differences\nbehind unstable aluminum anode cycling in symmetrical cells and AIBs,\nthe uniform removal of electrochemically inactive SEI components,\ne.g., oxide-rich or solvent-derived organic-rich interphases, leads\nto more efficient cycling behavior. These understandings raise the\nimportance of using specific conditioning protocols for efficient\ncycling of the aluminum anode in conjugation with different cathode\nmaterials.