Entropy-Regulated Cathode with Low Strain and Constraint Phase-Change Toward Ultralong-Life Aqueous Al-Ion Batteries

During multivalent ions insertion processes, intense electrostatic interaction between charge carriers and host makes the high-performance reversible Al³⁺ storage remains an elusive target. On account of the strong electrostatic repulsion and poor robustness, Prussian Blue analogues (PBAs) suffer severely from the inevitable and large strain and phase change during reversible Al³⁺ insertion. Herein, we demonstrate an entropy-driven strategy to realize ultralong life aqueous Al-ion batteries (AIBs) based on medium entropy PBAs (ME-PBAs) host. By multiple redox active centers introduction, the intrinsic poor conductivity can be enhanced simultaneously, resulting in outstanding capabilities of electrochemical Al³⁺ storage. Meanwhile, the co-occupation at metal sites in PBA frameworks can also increase the M-N bond intensity, which is beneficial for constraining the phase change during consecutive Al³⁺ reversible insertion, to realize an extended lifespan over 10,000 cycles. Based on the calculation at different operation states, the fluctuation of ME-PBA lattice parameters is only 1.2 %. Assembled with MoO₃ anodes, the full cells can also deliver outstanding electrochemical properties. The findings highlight that, the entropy regulation strategy could uncover the isochronous constraint on both strain and phase transition for long-term reversible Al³⁺ storage, providing a promising design for advanced electrode materials for aqueous multivalent ions batteries.