Recent progress on iron-based hexacyanoferrates for advanced potassium-ion batteries

Potassium-ion batteries (PIBs) are regarded as promising candidates for large-scale grid energy storage owing to the abundant reserves of potassium resources. Iron hexacyanoferrate (FeHCF), a type of Prussian blue analogue, has garnered significant attention as a cathode material for PIBs due to its robust open framework, high theoretical capacity, and cost-effectiveness. However, the practical application of FeHCF is hindered by its intrinsic limitations, including low electronic conductivity, the presence of interstitial water, and lattice vacancies, which collectively result in inadequate reversible capacity, poor cycling stability and unsatisfactory rate performance. In this review, we summarize the recent achievements of FeHCF cathode materials for PIBs, as well as the key challenges hindering their practical application. In addition, we discuss various modification strategies aimed at enhancing the potassium storage performance, categorizing them into direct approaches (e.g., structural modulation and transition metal doping) and indirect methods (e.g., morphology control, compositing with conductive materials and electrolyte modification). Finally, prospective research directions for improving the electrochemical performance of FeHCF are proposed. This review aims to offer insightful guidance for the rational design of advanced FeHCF materials for high-performance PIBs.