Tailored the polymer interface of Prussian blue analogues for sodium-ion batteries

Abstract

The development of long-life sodium-ion batteries (SIBs) hinges on stable cathode–electrolyte interfaces. Fe-based Prussian blue analogues (PBAs) are promising cathodes for SIBs, valued for their low cost and open framework that facilitates rapid three-dimensional Na⁺ diffusion. However, their practical application is severely limited by poor long-term cycling stability, a challenge primarily attributed to the formation of a fragile and chemically unstable cathode–electrolyte interphase (CEI). This natural CEI promotes parasitic side reactions that consume active Na⁺ inventory, increase interfacial impedance, and accelerate capacity fade. Here, we introduce a strategy to overcome this limitation by engineering a conformal, and nanoscale artificial CEI using a functionalized linked polymer (FLP). This engineered interphase acts as a robust physical and chemical barrier, effectively suppressing parasitic electrolyte decomposition, mitigating active material dissolution, and preserving the structural integrity of the cathode by buffering against chemo-mechanical strain. These findings establish key design principles for artificial CEIs, emphasizing conformality, mechanical compliance, and controlled thickness, providing a scalable route to high-performance, long-life Na-ion cathodes.