Revealing potassium ion storage in individual Prussian blue nanoparticles with distinct crystallinity via scanning...

Potassium-ion batteries (KIBs) have gained tremendous attention due to the abundance and low cost of potassium resources. However, challenges such as significant voltage hysteresis and sluggish diffusion kinetics require a deep understanding of ion storage in the cathode materials. This study investigates the intrinsic electrochemical properties of Prussian blue (PB) nanoparticles, promising cathode materials for KIBs, through single-particle measurements using scanning electrochemical cell microscopy (SECCM). PB nanoparticles with varying crystallinity were prepared by controlling the amount of polyvinylpyrrolidone (PVP) used as a chelating ligand during synthesis. Our findings reveal that PB nanoparticles with lower crystallinity displayed poor K⁺ storage properties, while excessive PVP adsorption on nanoparticle surfaces hampers electrochemical performance. Notably, PB nanoparticles prepared with trace amounts of PVP exhibit significantly enhanced K⁺ storage capabilities due to optimized structural integrity. This research highlights the critical role of particle crystallinity and surface chemistry in tailoring the performance of energy storage materials, providing insights for the design of advanced KIB systems.