Entropy-Stabilized Layered K0.6Ni0.05Fe0.05Mg0.05Ti0.05Mn0.725O2 as a High-Rate and Stable Cathode for Potassium-Ion Batteries

Abstract

Mn-based layered oxides have been considered the most promising cathode candidates for cost-effective potassium-ion batteries (PIBs). Herein, equiatomic constituents of Ni, Fe, Mg, and Ti have been introduced into the transition metal layers of Mn-based layered oxide to design a high-entropy K_0.6Ni_0.05Fe_0.05Mg_0.05Ti_0.05Mn_0.0725O₂ (HE-KMO, S = 1.17R). Consequently, the experimental results manifest that the layered structure of HE-KMO is more stable than conventional low-entropy K_0.6MnO₂ (LE-KMO, S = 0.66R) during successive cycling and even upon exposure to moisture. Diffraction and electrochemical measurements reveal that HE-KMO undergoes a solid-solution mechanism, contrary to the multistage phase transition processes typically exemplified in K_0.6MnO₂. Benefiting from the stabilized high-entropy layered framework and the solid-solution K⁺ storage mechanism, the entropy-stabilized HE-KMO not only demonstrates exceptional rate capability but also shows excellent cyclic stability. Notably, a capacity retention ratio of 86% after 3000 cycles can still be sustained at a remarkable current density of 5000 mA g^–1.