Intrinsic vacancy chemistry in Prussian white cathodes: origins, multiscale characterization, and electrochemical consequences

Abstract

AbstractPrussian White (PW) has emerged as a highly attractive cathode for sodium- and potassium-ion batteries. Nevertheless, conventional co-precipitation process unavoidably generates intrinsic structural defects, most prominently [Fe(CN)6] vacancies (VFeCN), which severely compromise electrochemical behavior. Owing to their thermodynamic favorability and kinetic persistence, simply minimizing vacancy formation is insufficient. Instead, a comprehensive understanding of vacancy generation mechanisms, structural functions, and degradation behaviors is imperative for rational material optimization. This review systematically analyzes the nature and origins of intrinsic defects in PW, including VFeCN, transition-metal (TM) vacancies (VTM), and cyanide ligand vacancies (VCN), with particular emphasis on synthesis conditions governing VFeCN formation. Furthermore, a multidimensional and multiscale defect characterization framework is established, encompassing electronic structure, local coordination environments, crystallographic ordering, and mesoscale morphology.Importantly, the review elucidates the direct links between vacancy chemistry and electrochemical behavior. VFeCN defects diminish available alkali-ion storage sites, interrupt continuous ion diffusion pathways, and promote interfacial parasitic reactions, resulting in capacity decay, sluggish kinetics, shortened cycle life, inferior low-temperature behavior, and compromised thermal stability. By integrating intrinsic defect chemistry with macroscopic electrochemical outcomes, this work offers a defect-informed roadmap for the design of durable and high-performance PW cathodes.