Lanthanide Contraction Builds Better High‐Voltage LiCoO2 Batteries

Abstract Cycling lithium cobalt oxide (LiCoO 2 ) to a potential higher than 4.35 V (vs Li + /Li) can obtain an enticing capacity, but suffers from inferior structural stability. Herein, an ingenious Li‐deintercalation/doping strategy is developed to synthesize the lanthanide‐doped LiCoO 2 (lanthanide (Ln) = praseodymium, neodymium, samarium, europium, gadolinium, erbium, or lutetium) with Ln occupying Li‐sites. Electrochemical measurements show that the cycling stability of Ln‐doped LiCoO 2 increases as the lanthanide contracts. By rule, lutetium‐doped LiCoO 2 exhibits the best cycling stability, confirmed in both lithium half‐cell and pouch full‐cell. Comprehensive experimental characterizations combining with theoretical calculations reveal that the lattice strain tuned by the lanthanide contraction plays a critical role in the structure stability of LiCoO 2 . This finding is an important step for building better high‐voltage LiCoO 2 batteries, as it is possible to achieve better high‐voltage performance by combining the doping technology and performance improvement rule disclosed in this study.