Stabilizing the aluminum metal anode through polymer coating-enabled regulation of exchange current†

Abstract

Aluminum-ion (Al-ion) batteries are emerging as promising candidates for large-scale energy storage due to their low cost. However, the poor cycling stability of the aluminum (Al) metal anode, which arises from more severe non-planar deposition than those of the other metals, particularly at high current densities, limits their practical applications. Herein, we applied classical metal electrodeposition theory to better understand aluminum deposition behavior and proposed a simple and practical approach to achieve uniform electrodeposition of aluminium. This approach involved regulating the ratio of exchange current density (i₀) to limiting current density (i_L), which serves as a descriptor for the metal deposition process. The regulation was achieved by applying an electron-insulating polydimethylsiloxane (PDMS) coating. By carefully tuning the coating thickness, we were able to regulate the exchange current density, optimizing the balance between mitigating interphase reactions and maintaining efficient mass transport. As a result, a stable Al metal anode reaction was obtained over 2800 hours under the exceptionally large current density of 5 mA cm⁻² and a high deposition capacity of 5 mA h cm⁻². The full cell with an artificial graphite cathode delivered a stable discharge capacity of 65 mA h g⁻¹ and a high CE of 99.5%, with no apparent capacity or CE decay over 2500 cycles. This work presents a new strategy for regulating electrodeposition in Al metal anodes and demonstrates an electrodeposition principle for metal anode batteries.