Safe Lithium-Metal Anodes for Li-O2 Batteries: From Fundamental Chemistry to Advanced Characterization and Effective Protection

Rechargeable Li-O-2 batteries play an increasing important role as energy storage devices, which have both, a high capacity anode and a cathode using an inexhaustible resource. As a key component in Li-O-2 batteries, the Li-metal anode suffers from major drawbacks related to Li dendrite formation and SEI layer growth, which are also major issues for Li-metal rechargeable batteries. This review presents an overview on the scientific challenges, fundamental mechanisms and modification strategies of Li-metal anodes for Li-O-2 batteries. Firstly, basic principles and challenges on Li-metal anodes are briefly retrospected. We further summarize and categorize the prevailing characterization techniques based on Li dendrite morphology characterization and SEI composition analysis. The up-to-date development of in-situ and operando characterization is also included. Following the obtained insights, effective protection/modification strategies towards practical application for Li-O-2 batteries are presented. Furthermore, we highlight the significance of advanced characterization techniques in interrogating the buried keys for solving practical hindrances for Li-O-2 batteries. The comprehensive characterization and analysis of Li anodes, cathodes, and electrolytes by various methods together with the development of novel techniques are expected to be indispensable to gain a thorough understanding of the battery operation and for offering guidelines for their practical development.