Entropy-Stabilized\nLayered K_0.6Ni_0.05Fe_0.05Mg_0.05Ti_0.05Mn_0.725O₂ as a High-Rate and\nStable Cathode for Potassium-Ion\nBatteries

Abstract

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