In situ surface manipulation Mn-based Prussian blue analogues with enhanced redox chemistry and ion diffusion toward high-energy-density aqueous sodium-ion batteries

Abstract

Manganese-based Prussian blue analogues (Mn-PBA) are promising cathode materials for aqueous sodium-ion batteries (ASIBs) owing to their open framework that facilitates efficient sodium ion insertion/extraction. However, their practical deployment is hindered by structural collapse arising from high-spin Mn³⁺ (HS-Mn³⁺) dissolution during cycling, triggered by the Jahn–Teller effect, which severely limits long-term stability. Here, we design an in situ chemically regulated Mn@Fe/H-PBA electrode with a hierarchical hollow structure via co-precipitation. The hollow architecture provides a large surface area for enhanced active site utilization, while the stabilized hierarchical framework enriched with low-spin Mn³⁺ (LS-Mn³⁺) effectively suppresses structural distortion. Together, these features enable Mn@Fe/H-PBA to deliver a high discharge capacity of 121 mA h g⁻¹ at 1 A g⁻¹ with excellent cycling durability. In situ/ex situ characterization combined with density functional theory (DFT) calculations confirm the improved redox activity and mitigated Jahn–Teller distortion. Full cells paired with a polyimide (PI) anode achieve an energy density of 74.32 W h kg⁻¹, while pouch cells demonstrate stable cycling over 500 cycles at 1 A g⁻¹. This work provides a robust strategy to overcome stability challenges in Mn-PBA cathodes for next-generation ASIBs.