Stabilizing aluminum metal anode with exchange current regulation

Abstract

Aluminum-ion (Al-ion) batteries are up-and-coming batteries for large-scale energy storage due to their low cost. However, the poor cycling stability of the aluminum (Al) metal anode arising from much more severe non-planner deposition than the other metals, especially at high current densities, limits their practical applications. Herein, we use classical metal electrodeposition theory to understand the aluminum deposition behavior and show a simple and practical way, that is, regulating the exchange current density (i0)/limiting current density (iL), the descriptor for metal deposition behavior, for uniform electrodeposition of aluminum metal. The regulation is realized by an electron-insulating polydimethylsiloxane (PDMS) coating. By carefully tuning the coating thickness, we can regulate the exchange current density to optimally balance mitigating interphase reactions while maintaining efficient mass transport. As a result, a stable Al metal anode reaction over 2800 hours is obtained under the exceptionally large current density of 5 mA cm-2 and a large deposition capacity of 5 mAh cm-2. The full cell with artificial graphite cathode delivers a stable discharge capacity of 65 mAh g-1 and a high CE of 99.5 %, without apparent capacity or CE decay over the 2500 cycles. This work presents a new strategy for regulating electrodeposition for Al metal anode and demonstrates an electrodeposition principle for metal anode batteries.