Layer-structured K0.5Mn0.8Cu0.1Mg0.1O2 for high-performance potassium-ion batteries by alleviating the phase transformation

Abstract

Manganese-based layered oxide is a promising candidate for cathode material in potassium-ion batteries (KIBs). It suffers from the Jahn–Teller distortion, particularly when working at high voltage regimes, the cycling lifespan cannot satisfy the increasing demand resulting from the frequent phase transformation and significant volume variations. The orbital and electronic structure of the metal element in the octahedral center plays an important role in maintaining the structural integrity and improving the K⁺ diffusivity. By intruding the [Mn–Cu–Mg]–O6 octahedral to optimize the local electron structure in oxygen, the K_0.5Mn_0.8Cu_0.1Mg_0.1O₂ cathode possesses an expanded layer spacing and enhanced structural stability. The voltage decay phenomenon is alleviated as well when charged to higher voltages. The simultaneous substitution of Cu and Mg effectively inhibits the phase transformation from O3 to P′′3, resulting in a smoother phase transformation between 3.5 and 4.0 V. This indicates that the [Mn–Cu–Mg]–O6 octahedral can not only decrease the amount of Mn(III) and suppress the Jahn–Teller effect by reducing the redox activity of Mn^3+/4+, but also improve the cyclic stability of the layered cathode by regulating the K⁺/vacancy ordering.