Understanding Degradation and Enhancing Cycling Stability for High-Voltage LiCoO2-Based Li-Metal Batteries

Abstract

Improving the energy density of Lithium (Li)-ion batteries (LIBs) is vital in meeting the growing demand for high-performance energy storage and conversion systems. Developing high-voltage LIBs using high-capacity and high-voltage cathode materials is promising for enhancing energy density. However, conventional cathode and electrolyte materials face serious decomposition and structural degradation at high operating voltages. Herein, a dual-salts electrolyte of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide(LiFSI-LiTFSI) is developed to improve the cycling stability of high-voltage lithium cobalt oxide (LiCoO2, LCO)||Li batteries. Operando X-ray diffraction analysis experiments are carried out to characterize the structural stability of cathode materials, suggesting a severe irreversible phase transformation at high voltage levels. Aging simulations, combined with experimental studies, suggest that a fast loss of active materials is mainly responsible for the capacity loss at high voltages. Carbon-coated LCO cathodes are synthesized to mitigate cycling degradation. The designed LCO||Li cells exhibit a high-capacity retention of over 85% after 400 cycles at 4.7V. The present work provides a novel insight into understanding the degradation and enhancing the stability of high-voltage LCO-based Li-metal batteries, thus facilitating their practical applications.