Decoding the functional roles of multimetallic constituents in high-entropy prussian blue analogues for sodium-ion batteries.

Prussian blue analogues (PBAs) have emerged as promising cathode materials for sodium-ion batteries (SIBs) due to their low cost, simple preparation, and high theoretical specific capacity. The integration of high-entropy concepts with framework-structured PBAs has pioneered a new pathway for performance optimization in SIBs cathodes. However, most scholars have only studied the five elements constituting high entropy as a whole, while challenges such as the role of each element and optimization of the proportions among constituent elements remain unresolved. This report presents high-entropy non-equimolar PBAs and investigates the functional roles of constituent elements (Fe, Mn, Ni, Cu, Zn). Through continuous optimization of elemental ratios, the optimal sample PB-FM1-Ni2 demonstrates exceptional performance: delivering an initial discharge capacity of 122.7 mA h g at 0.1 C, maintaining 78.0 mA h g after 800 cycles at 1 C (corresponding to 72.0 % capacity retention), and exhibiting outstanding rate performance (86.0 mA h g at 30 C). Furthermore, distribution of relaxation times (DRT) analysis reveals the impedance characteristics of the materials, while in situ techniques clarify a highly reversible two-phase sodium-ion storage mechanism. Finally, full cells assembled with hard carbon (HC) anodes and the prepared cathodes exhibit excellent compatibility, demonstrating strong potential for applications in large-scale energy storage systems.