Multiscale binder engineering enables high-kinetics Prussian blue analogue cathodes for aqueous Na-ion batteries

Abstract

Aqueous Na-ion batteries (ANIBs) are promising candidates for grid-scale energy storage owing to their inherent safety, low cost, and rapid ion transport kinetics. While current research focuses on enhancing capacity and kinetics to overcome energy density limitations and leverage their inherent kinetic advantages under extreme conditions such as high mass loading and low temperatures, investigations remain predominantly centered on electrode materials and electrolytes, with binders being notably understudied. Here, we investigate the impact of two prevalent binders-polyvinylidene difluoride (PVDF) and polytetrafluoroethylene (PTFE)-on the electrochemical performance of nickel hexacyanoferrate (NiHCF) electrodes in ANIBs. Our results reveal that PVDF's better adhesion and electrolyte wettability optimize ion transport, significantly enhancing electrode kinetics vs. PTFE. Utilizing PVDF as the binder in a 3D-printing platform, we fabricated a freestanding electrode achieving >20 mg cm⁻² active material loading, superior kinetics, and >95% capacity retention over 4000 cycles. The derived full cell reduces polarization at −20 °C, delivering higher energy density than PTFE-based full cells. This work demonstrates a multiscale regulation strategy for binder-electrode structures, offering a viable pathway toward high-performance aqueous energy storage systems.