Topological Insulator Bi2Te3 Anode for Aqueous Aluminum-Ion Batteries: Unveiling the Role of Hydronium Ions

Abstract

The primary scientific challenge in advancing aqueous aluminum-ion batteries (AAIBs) is achieving reversible plating/stripping of the Al metal anode, limited by its low deposition potential (-1.667 V vs SHE) and surface passivation in the aqueous electrolyte. To address this issue, polypyrrole (PPy) decorated topological quantum insulator (Bi2Te3@PPy) is introduced as a novel anode in AAIBs. Benefiting from the interconnected PPy network and the gap-free metallic surface state of Bi2Te3, the Bi2Te3@PPy anode enables a remarkable discharge capacity of 438 mAh g-1 at a current rate of 0.5 A g-1. It also maintains a strong discharging plateau even at a higher current rate of 10 A g-1, outperforming most electrode materials reported so far for AAIBs. The role of the topological surface states of Bi2Te3 in enhancing the ion migration rate is validated by comparing its performance across various morphologies. Ex situ studies and computational analysis reveal that in aqueous systems, Al3+ is not the sole species responsible for charge storage. Instead, hydronium ions (H3O+) significantly contribute to storing the charges through intercalation into the crystal lattice. Overall, this study pioneers a new approach for developing advanced Al metal-free AAIBs and provides deeper insights into the charge storage mechanisms in aqueous electrolytes.