Abstract
In the search for materials used as active species in cathodes for K-ion batteries, only few compositions of transition metal oxides or transition metal polyanionic frameworks have been proposed so far. In this work, we report for the first time the synthesis and study of the electrochemical activity an original K3MnO4 polymorph. This phase is a 0D-type structure made of isolated MnO4 tetrahedra surrounded by K+ ions. A reversible charge capacity of almost one K+ per unit formula at the average voltage of 2.3 V vs. K+/K is obtained, leading to the reversible formation of K2MnO4 through a biphasic process.