High‐Entropy Gradient‐Like Design Enables 4.7 V High‐Stability LiCoO 2 for Lithium‐Ion Battery

ABSTRACT High‐voltage LiCoO 2 (LCO) is considered as the solution to extend the battery life of smart electronic devices. However, it still suffers from severe interface instability and structural degradation above 4.7 V. Herein, we put forward a high‐entropy gradient‐like design via high‐entropy (TiO 2 , Al 2 O 3 , MgO, In 2 O 3 , and La 2 O 3 ) surface coating that combines an ultra‐thin high‐entropy coating layer of 1.35 nm thickness and subsurface gradient‐like doping of 1 nm depth. This surface structure can suppress side reactions and enhance Li + diffusion kinetics on the surface. Also, subsurface gradient‐like doping restrains lattice distortion from the irreversible O3‐H1‐3‐O1 phase transition so as to strengthen the electrochemical stability above 4.7 V. A series of in situ, ex situ characterizations and DFT calculations fundamentally clarify the optimized structure‐activity relationship and electronic/spatial effects. Hence, this high‐entropy lattice designed LCO displays a superior capacity of 197.24 mA h g −1 at 1C with 92.4% capacity retention during 400 cycles within 3.0–4.7 V in half‐cells. Moreover, when cycled in a full LCO//graphite pouch‐cell, it can show a competitive cycling capacity of 210.42 mA h g −1 at 0.5C and stability of 95.5% after 100 cycles during 3–4.6 V, manifesting strong practicality in high‐volumetric‐energy‐density and long‐lasting LCO materials.