Suppressing Jahn-Teller distortion and phase transition of K0.5MnO2 by K-site Mg substitution for potassium-ion batteries

In the development of cathode materials for potassium-ion batteries, K0.5MnO2 cathode has shown great potential due to its high capacity and high energy density. However, it suffers from poor cycle stability due to the strong Jahn-Teller effect of Mn3+ and structure degradation. Here, by introducing Mg into the potassium layer, we design a new layered P3-type K0.5Mg0.15[Mn0.8Mg0.05]O2 cathode material. By using X-ray diffraction and absorption techniques, it is revealed that Mg ions in potassium layer can not only suppress the Jahn-Teller effect and prevent phase transition effectively, but also enhance the kinetics and thermodynamic properties of the cathode materials, thus greatly improve the cycle stability and rate capability. The strategy may open a new opportunity to design layered cathode materials for high performance potassium-ion batteries.