FeOHSO@C Cathode with Low Strain and High Pseudocapacitance for Advanced Potassium-Ion Batteries.

Iron-based polyanionic cathode materials in potassium-ion batteries (KIBs) have appealed to an increasing number of interest due to these advantages of low cost, environmental friendliness and excellent structural stability. However, these inherent drawbacks of inferior electronic conductivity and terrible nanostructural stability hinder its practical application. Here, we report a novel low-strain iron-based polyanion-type cathode material FeOHSO@C for KIBs. In this work, the surface of FeOHSO nanoparticles is well carbon encapsulated, carbon coating layer with large surface area and excellent electrical conductivity is ≈2.5 nm in thick, which can not only inhibit the aggregation and growth between FeOHSO@C nanoparticles during charging and discharging, but also provide a 3D electronic conductive framework that activates electrochemical reactivity. As a result, the FeOHSO@C cathode exhibits outstanding potassium storage capacity (capacity retention of 80.95% over 200 cycles at 20 mA g) attributed to a low-strain mechanism for K uptake/removal, high pseudocapacitance, as well as 3D electronic conductive framework. Operando XRD and ex situ XPS analyses revealed a single-phase reaction route of orthorhombic FeOHSO@C during cycling.