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

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.