High Entropy-Induced Kinetics Improvement and Phase Transition Suppression in K-Ion Battery Layered Cathodes
Shiyong Chu, Caoyang Shao, Jiaming Tian, Jingyang Wang, Yuan Rao, Chengrong Xu, Haoshen Zhou, Shaohua Guo
Abstract
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 K 0.45 Mn 0.60 Ni 0.075 Fe 0.075 Co 0.075 Ti 0.10 Cu 0.05 Mg 0.025 O 2 (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 K 0.45 MnO 2 (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.