Studying the failure mechanism in Li-metal electrode by a reversible fluorescence analysis methodology

Elucidating the failure mechanisms of Li metal electrodes is critical to accelerating the development of long cycle life Li metal batteries. However, it has not yet fully been realized so far due to the challenges associated with quantitative and qualitative characterization of solid electrolyte interphase on metal at large-area scale. Herein, we establish a relationship between solid byproducts and dead Li amounts in solid electrolyte interphase on Li metal by using fluorescence imaging and fluorescence titration method. The success of this methodology depends on the finding of a highly selective molecular probe, dilithium 3-hydroxy-2-naphthoate, with reversible change in fluorescence wavelength and intensity toward Li metal. Accordingly, the continuous generation of solid byproducts is acknowledged as potential underlying reason towards dead Li accumulation, determining the failure of Li electrode. These findings provide insights into the understanding of failure mechanism of Li metal electrode and design of strategies to improve its cycle life. Understanding Li electrode failure is challenged by efficient evaluation of solid electrolyte interphase. Here, authors develop a qualitative and quantitative fluorescent method to correlate solid byproducts and accumulated dead Li in the solid electrolyte interphase, identifying the underlying role of side reactions.