Research progress of manganese-based layered oxides as cathode materials for potassium-ion batteries

Potassium is inexpensive, abundant, and evenly distributed in the Earth's crust. It has similar physical and chemical properties to those of lithium. Therefore, the use of potassium-ion batteries is expected to be realized. Cathode materials are important components of potassium-ion batteries. In addition to potassium-containing compounds, other cathode materials should be actively explored. Manganese-based oxides are widely used as cathode materials in various batteries because of their multiple ion valence states, abundant mineral reserves, low cost, and convenient synthesis methods. Among these various cathode materials manganese dioxide with a layered structure has a large interlayer spacing, which can be used for the insertion and extraction of potassium ions with a large ionic radius between the layers. Therefore, layered KxMnO2 (KMO) cathode materials have significant potential for development. This paper reviews the research status of manganese-, ferromanganese-, manganese magnesium-, nickel manganese-, nickel cobalt manganese-, and iron titanium manganese-based metal oxides as cathode materials for potassium-ion batteries. Additionally, the obstacles and opportunities faced by KMO materials as cathode materials for potassium-ion batteries are comprehensively discussed.