Characterizing the Role of Fluoroethylene Carbonate (FEC) in Suppressing the Nucleation and Growth of Plated Lithium in Fast-Charged Lithium Ion Battery Systems*

For decades, the high energy density, superior longevity, and low maintenance costs afforded by lithium ion batteries (LIBs) have made them a staple of the consumer electronics industry. However, shifts in large scale energy demands driven by booming electric vehicle and renewable energy markets have exposed the limitations of modern LIB designs. Specifically, transport limitation-driven lithium plating at the anode-electrolyte interface during fast charging, resulting in capacity fade, internal shorting, and the potential for thermal runaway, continues to inhibit the growth of these and other industries. This work focuses on the use of nondestructive, in situ synchotron hard X-ray microtomography (XRM) to study the influence of a promising electrolytic additive, fluroroethylene carbonate (FEC), on the nucleation and growth mechanisms of plated lithium in fast charged LIB systems. Through a bottom-up, data-driven approach, we study and compare the morphology, prevalence, and heterogeneity of plated lithium at the anode-electrolyte interface in non-FEC and FEC systems at the sub-micron scale to both quantify and explain the efficacy of this additive in improving the performance and safety of LIBs. As such, we develop a novel framework for systematically screening novel electrolytic mixtures to bolster and expand upon the insights offered by conventional ex situ approaches that can be readily applied to the research and development of other "alternative" LIB designs and architectures.