Lanthanide Contraction Builds Better High-Voltage LiCoO2 Batteries

Cycling lithium cobalt oxide (LiCoO2) 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 LiCoO2 (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 LiCoO2 increases as the lanthanide contracts. By rule, lutetium-doped LiCoO2 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 LiCoO2. This finding is an important step for building better high-voltage LiCoO2 batteries, as it is possible to achieve better high-voltage performance by combining the doping technology and performance improvement rule disclosed in this work.