Investigation on Al3+ ion storage in Bi2MoO6 and Bi2WO6 for rechargeable aqueous aluminum-ion battery

Reversible and stable electrochemical Al3+ ion storage process defines the functioning of a rechargeable aluminum-ion battery. Herein, we illustrate the electrochemistry of Bi2MoO6 and Bi2WO6 for Al3+ ion storage in aqueous electrolyte. It was found that the electrochemical characteristics are quite dependent on the nature of the electrolyte. While the charge-discharge profiles are almost identical for both Bi2MoO6 and Bi2WO6, it is to be noted that Bi2WO6 exhibits better electrochemical long-term stability and severe capacity decline is noticeable for Bi2MoO6. The specific discharge capacity is 94 mAhg- 1 at a current density of 1 Ag-1 over 50 cycles for Bi2WO6 in an optimized AlCl3 aqueous electrolyte. By adopting an optimized current collector, the specific capacity could be significantly enhanced to above 200 mAhg- 1 at a current density of 1 Ag-1. A mechanistic study conducted through ex-situ XRD, XPS, Raman, FTIR, UV-Visible, FESEM and HRTEM reveals probable transformation of Bi2WO6 to BiOCl during the electrochemical process.