Surface Design with Cation and Anion Dual Gradient Stabilizes High‐Voltage LiCoO2

Abstract

AbstractLiCoO2(LCO) is the most successful cathode material for commercial lithium‐ion batteries. Cycling LCO to high potentials up to 4.5 V or even 4.6 V can significantly elevate the capacity but cause structural degradation due to the serious surface side reaction between the highly oxidized Co4+and O−species with organic electrolytes. To tackle this concern, a new strategy, constructing cation and anion dual gradients at the surface of LCO (DG‐LCO), is proposed. Specifically, the electrochemically inactive cation and anion are selected to substitute Co3+and O2−at the surface in a gradated manner, thus minimizing the highly oxidized Co4+and O−species at high potentials and suppressing the induced surface side reactions. Unexpectedly, this dual gradient design leads to a spinel‐like surface structure coherently with bulk layered structure, which facilitates Li+diffusion kinetics. Thus, DG‐LCO achieves high capacity and excellent cycling stability at 4.6 V (≈216 mA h g−1at 0.1 C, a capacity retention of 88.6% after 100 cycles in 1.8 A h pouch full cell at 1 C), as well as improved rate capability (≈140 mA h g−1at 5 C). These studies provide useful guidelines for future design of cathode materials with long lifespan and high rate capability.