Initial-anode-free aluminum ion batteries: In-depth monitoring and mechanism studies

Rechargeable aluminum-ion batteries have attracted great attention due to the high theoretical volumetric capacity, good safety and abundant sources. Although tremendous efforts have been concentrated on exploring novel electrode materials for aluminum-ion batteries, the electrochemical mechanism still need to be further investigated. In this work, we found that even without employing any initial anode materials, the aluminum-ion batteries assembled with graphite cathode, AlCl3/ion liquid based electrolyte and various anodic current collectors still can be stably charged/discharged. A variety of carbon or metal based materials can be utilized as anodic current collectors in the initial-anode-free aluminum-ion batteries; however, their anti-corrosion capabilities against Cl− ions do greatly affect the battery performances. The electrochemical mechanism of initial-anode-free aluminum-ion batteries were comprehensively investigated by a series of in-situ and ex-situ spectroscopic and microscopic methods, revealing the reversible Al metal plating/stripping processes on the anodic current collectors during the charge-discharge cycles. We hope this work may provide new insights into the key component design and mechanism study of initial-anode-free multivalent secondary batteries.