Lanthanide contraction builds better high-voltage LiCoO${}_2$ batteries

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. (© 2022 Wiley‐VCH GmbH)