FeOHSO4@C Cathode with Low Strain and High Pseudocapacitance for Advanced Potassium-ion Batteries.

Abstract

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 FeOHSO4@C for KIBs. In this work, the surface of FeOHSO4 nanoparticles are well carbon encapsulated, carbon coating layer with large surface area and excellent electrical conductivity is ~2.5 nm in thick, which can not only inhibits the aggregation and growth between FeOHSO4@C nanoparticles during charging and discharging, but also provides a three-dimensional (3D) electronic conductive framework that activates electrochemical reactivity. As a result, the FeOHSO4@C cathode exhibits outstanding potassium storage capacity (capacity retention of 80.95% over 200 cycles at 20 mA g-1) 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 FeOHSO4@C during cycling.