Tuning Co/O Redox Chemistry via Fermi Level Regulation for Stable High-Voltage LiCoO<sub>2</sub>
Mingpu Wen, Weijin Kong, Jicheng Zhang, Qinghua Zhang, Wen Yin, Nian Zhang, Ke Chai, Yang Yu, Huaican Chen, Xiangfeng Liu
Abstract
LiCoO2 (LCO) is ideal for 3C electronics due to its high tap density. However, the excessive O → Co charge transfer at high delithiation leads to irreversible Co reduction, O release, and structural degradation, deteriorating the high-voltage performance of LCO. Herein, we propose to regulate the intrinsic Fermi level via uneven trace Zr/Mg doping. First, the increase of electron density in the Fermi level mitigates both the O oxidation/coupled Co reduction through alleviating the O → Co charge transfer, restraining the formations of Co2+ and O2. This elevates Co redox activity and reduces O redox activity. In addition, the structural evolution of the cathode at delithiation is simplified. The modulated LCO delivers a high discharge capacity and a high cycling stability with 4.5 and 4.6 V ceilings. This study sheds new light on the modulation of Co/O redox chemistry and the reliable large-scale production of high-voltage LiCoO2.