Modulating Surface Structural Evolution of LiCoO2 for Enhanced Extreme Fast-Charging Durability.

Abstract

The applied cathodes in lithium-ion batteries usually suffer from severe structural degradation upon fast charging, and the correlated mechanism still remains vague. Here, we reveal the surface structural evolution of LiCoO2 (LCO) during cycling at 4.6 V vs Li/Li+ with an extreme high fast-charging current of 10 C. Fast charging induces surface heterogeneous delithiation, promoting nonuniform surface phase transitions and resulting in the formation of a triphase hybrid on the charged surface. The triphase hybrid consists of the layered, spinel, and rock-salt (RS) phases. As cycling proceeds, this triphase hybrid propagates gradually toward the bulk, accompanied by a progressive thickening of the surface RS phase, leading to deteriorated Li+ transport kinetics and accelerated capacity fading. Thus, suppressing the heterogeneous Li+ delithiation of LCO is crucial for enhancing fast-charging durability. By applying a uniform and robust surface coating, the surface delithiation homogeneity upon extreme fast charging is significantly improved, and the thickening of the surface Li+-blocking RS phase is greatly reduced, thereby achieving enhanced cycling stability of LCO. This work benefits the development of more advanced LCO cathodes tailored for fast-charging applications.