δ‐MnO2/KMnF3 Composite with Mixed Valence as Cathode for Potassium Ion Battery

Abstract

AbstractPotassium ion batteries (PIBs) are regarded as potentially promising large‐scale energy storage systems. δ‐MnO2/KMnF3‐30 (mass percentage of KMnF3: 30%) with mixed valence of manganese is constructed by homogeneous precipitation method, as cathode for PIBs. As a buffer and chelating agent for the reaction, disodium ethylenediamine tetraacetate (EDTA‐2Na) is helpful to form composites with good mixing and uniform dispersion. δ‐MnO2 nanowires with different lengths can fully utilize the cross‐linking of long nanowires and short‐range filling of short nanowires, resulting in more stable network connectivity. Additionally, the uniform embedding of the KMnF3 nanoparticles among δ‐MnO2 nanowires can effectively accommodate the volume expansion associated with ion intercalation during cycling process. δ‐MnO2/KMnF3 combines the advantages of Mn‐based fluoride and Mn‐based oxide as cathode materials, and has high capacity, good cycle performance and rate performance. The capacity at a current density of 100 mA g−1 after 200 cycles can still be as high as 90 mAh g−1. Electrochemical impedance spectroscopy is used to study the reaction process of the δ‐MnO2/KMnF3 cathode at the electrode/electrolyte interface and to explain some electrochemical phenomena.