Layered oxides are widely accepted to be promising cathode
candidate
materials for K-ion batteries (KIBs) in terms of their rich raw materials
and low price, while their further applications are restricted by
sluggish kinetics and poor structural stability. Here, the high-entropy
design concept is introduced into layered KIB cathodes to address
the above issues, and an example of high-entropy layered K0.45Mn0.60Ni0.075Fe0.075Co0.075Ti0.10Cu0.05Mg0.025O2 (HE-KMO) is successfully prepared. Benefiting from the high-entropy
oxide with multielement doping, the developed HE-KMO exhibits half-metallic
oxide features with a narrow bandgap of 0.19 eV. Increased entropy
can also reduce the surface energy of the {010} active facets, resulting
in about 2.6 times more exposure of the {010} active facets of HE-KMO
than the low-entropy K0.45MnO2 (KMO). Both can
effectively improve the kinetics in terms of electron conduction and
K+ diffusion. Furthermore, high entropy can inhibit space
charge ordering during K+ (de)insertion, and the transition
metal–oxygen covalent interaction of HE-KMO is also enhanced,
leading to suppressed phase transition of HE-KMO in 1.5–4.2
V and better electrochemical stability of HE-KMO (average capacity
drop of 0.20%, 200 cycles) than the low-entropy KMO (average capacity
drop of 0.41%, 200 cycles) in the wide voltage window.