Mg-Substituted dual-walled Prussian blue analogous achieving enhanced active sites and stability for aqueous Al-ion batteries

Prussian blue analogues (PBAs) have emerged as promising candidates for aqueous aluminum-ion batteries (AAIBs) due to their unique open framework structure. However, the advancement of high-performance AAIBs is hindered by their limited capacity and significant capacity degradation, primarily due to inadequate redox-active sites and insufficient structural stability. To address this issue, this work employed tannic acid (TA) etching and cation exchange to synthesize Mg-substituted dual-walled Mn-PBA nanocubes (MgMn-PBA DWNCs), demonstrating their exceptional capability for Al 3+ storage. This unique dual-walled structure can expose abundant active sites and mitigates frequent volume changes during cycling. Besides, Mg-substituted effectively stabilizes the crystal framework and promotes the ionic diffusivity. The results show that MgMn-PBA DWNCs exhibit excellent rate performance and cycle stability, achieving a reversible capacity of 74 mAh g −1 at 4 A g −1. Ex-situ characterization and DFT simulation confirm that the superior Al 3+ storage mechanism of MgMn-PBA DWNCs can be attributed to the highly reversible redox reactions of transition metals, effectively enhanced structural stability, and significantly improved Al 3+ ionic diffusivity. Furthermore, a full battery comprising α-MoO 3 //MgMn-PBA DWNCs demonstrates remarkable cycling stability, maintaining a capacity of 78.6 mAh g −1 over 2000 cycles at 1 A g −1, corresponding to approximately 72.1 % capacity retention. This study offers a promising approach for the advancement of rechargeable AAIBs.