Diffusion-Optimized Long Lifespan 4.6V LiCoO2: Homogenizing Cycled Bulk-To-Surface Li Concentration with Reduced Structure Stress.

Abstract

Increasing the charging cut-off voltage (e.g., 4.6V) to extract more Li ions are pushing the LiCoO2 (LCO) cathode to achieve a higher energy density. However, an inhomogeneous cycled bulk-to-surface Li distribution, which is closely associated with the enhanced extracted Li ions, is usually ignored, and severely restricts the design of long lifespan high voltage LCO. Here, a strategy by constructing an artificial solid-solid Li diffusion environment on LCO's surface is proposed to achieve a homogeneous bulk-to-surface Li distribution upon cycling. The diffusion optimized LCO not only shows a highly reversible capacity of 212mAhg-1 but also an ultrahigh capacity retention of 80% over 600cycles at 4.6V. Combined in situ X-ray diffraction measurements and stress-evolution simulation analysis, it is revealed that the superior 4.6V long-cycled stability is ascribed to a reduced structure stress leaded by the homogeneous bulk-to-surface Li diffusion. This work broadens approaches for the design of highly stable layered oxide cathodes with low ion-storage structure stress.