Highly Stable Prussian White K₂MnFe(CN)₆–Carbon Nanotube Cathode for Advanced Potassium-Ion Batteries

The present study is focused on a composite material consisting of the Prussian white analogue K2MnFe(CN)6 (K-MnHCF) with modified carbon nanotubes (CNTs), used as a promising high-energy cathode for potassium-ion batteries (PIBs). The incorporation of the carbon network to the Prussian white analogue prepared through a facile chelating agent-assisted precipitation method provided control over the particle features, crystallization defects, and lattice moisture compared with the material prepared without it. Thus, at low current rates of 0.1 and 0.5 C in a given voltage window of 2.7–4.4 V vs K/K+, the K-MnHCF–CNT cathode showed a high reversible capacity of 119 mAh g–1, while the material without a CNT backbone delivered a capacity of 108 mAh g–1, exhibiting a capacity loss during cycling. Operando X-ray diffraction analysis demonstrated the stability of the K-MnHCF–CNT cathode, showing a reversible two-phase structural transition from monoclinic to tetragonal via an intermediate cubic phase. Moreover, the operando analysis revealed that the incomplete phase conversion from the intermediate cubic to tetragonal phase, related to the Mn2+/Mn3+ transition during charging in the K-MnHCF material without a carbon backbone, can be responsible for its structural instability. Ex-situ findings with the recovered active electrode supported the findings of the operando analysis. Thus, the K-MnHCF–CNT composite appears as a promising candidate for the development of suitable cathodes of PIBs for energy-storage applications.