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

Potassium ion batteries (PIBs) are regarded as potentially promising large-scale energy storage systems. delta-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. delta-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 delta-MnO2 nanowires can effectively accommodate the volume expansion associated with ion intercalation during cycling process. delta-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 delta-MnO2/KMnF3 cathode at the electrode/electrolyte interface and to explain some electrochemical phenomena.