(212f) Understanding the Chemistry and Formation of Fsi-Derived Solid-Electrolyte Interphase at Li-Metal Anode

Li metal battery (LMB) has always been considered as the holy grail to break the current limitations in energy density of Li-ion battery. However, commercialization of LMB has long been plagued by numerous operational issues such as Li dendrite formation causing safety concerns, as well as uncontrolled interfacial reactivity leading continuous electrolyte consumption.

Developing new liquid electrolyte based on ether solvent and LiFSI salt is a promising strategy of enhancing the reversibility of Li-metal anode (LMA), with the state-of-the-art values of Coulombic efficiency (CE) exceeding 99.5 %. Nevertheless, the chemical origin of Coulombic inefficiency (CI) and its correlation with the formation of solid-electrolyte interphase (SEI) at Li metal surface have not been well understood. A fundamental look at these basic processes accompanying the continuous cycling of LMA, can offer deep insights to rationally guide further optimization in CE.

In this talk, I will introduce our recent advances in systematically revealing the underlying chemistry and formation of FSI-derived SEI at the interface for Li metal anode in contact with various liquid electrolytes. Based on Cu current collector, we introduce a non-washing protocol of XPS analysis to capture and identify key reaction intermediates from SEI chemistry, allowing precise determination of decomposition pathway for FSI^- anion. Importantly, we reveal a highly dynamic picture at electrode/electrolyte interface where these reaction products can undergo significant dissolution into liquid layer, whereas their relative solubility determines their contribution towards electrode surface passivation. Further, we demonstrate higher-performing electrolytes exhibit faster interfacial passivation that strongly correlates with the reduced solubility of various inorganic species from electrode surface to liquid. These new insights into the SEI chemistry and formation will point out new directions of improving the LMA performance by minimizing side reactions at interface.