One‐Step Surface‐to‐Bulk Modification of High‐Voltage and Long‐Life LiCoO₂ Cathode with Concentration Gradient Architecture

Abstract Raising the charging cut‐off voltage of layered oxide cathodes can improve their energy density. However, it inevitably introduces instabilities regarding both bulk structure and surface/interface. Herein, exploiting the unique characteristics of high‐valence Nb⁵⁺ element, a synchronous surface‐to‐bulk‐modified LiCoO₂ featuring Li₃NbO₄ surface coating layer, Nb‐doped bulk, and the desired concentration gradient architecture through one‐step calcination is achieved. Such a multifunctional structure facilitates the construction of high‐quality cathode/electrolyte interface, enhances Li⁺ diffusion, and restrains lattice‐O loss, Co migration, and associated layer‐to‐spinel phase distortion. Therefore, a stable operation of Nb‐modified LiCoO₂ half‐cell is achieved at 4.6 V (90.9% capacity retention after 200 cycles). Long‐life 250 Wh kg⁻¹ and 4.7 V‐class 550 Wh kg⁻¹ pouch cells assembled with graphite and thin Li anodes are harvested (both beyond 87% after 1600 and 200 cycles). This multifunctional one‐step modification strategy establishes a technological paradigm to pave the way for high‐energy density and long‐life lithium‐ion cathode materials.