(265d) Electrolyte Additives for Surface Engineering (EASE) Inspired By Atomic Layer Deposition

Lithium metal batteries with liquid electrolytes have long been considered the holy grail for next generation energy storage. However, maintaining stability of the lithium metal anode has been the major challenge to achieve the required performance goals needed for commercialization. One promising approach of lithium surface engineering has been atomic layer deposition (ALD). Although ALD ensures extreme thickness control of surface coatings with angstrom scale precision, performing ALD directly on lithium is challenging and expensive.

In this work, we introduce electrolyte additives for surface engineering (EASE), with the additives inspired by atomic layer deposition (ALD). We show that by using traditional gas phase alkyl aluminum metal-organic ALD precursors as unconventional additives for liquid electrolyte engineering, we can achieve a highly stable lithium interface. We propose that EASE design with alkyl aluminum additives serves two main purposes. First, it forms an Al₂O₃ interfacial passivation layer atop lithium, as confirmed by X-ray photoelectron spectroscopy (XPS) and cryo-transmission electron microscopy (cryo-TEM). Second, it reacts away trace water in the electrolyte due to the water-reactive nature of the ALD precursors, as confirmed by nuclear magnetic resonance (NMR). Moreover, by sequentially varying precursor chemistry and concentration of the additive, we find correlations between the behavior in electrolyte with ALD precursor design principles. Notably, EASE facilitates the retention of the shiny metallic nature of lithium in air for at least 2 days, providing strong direct evidence of lithium stability. Although Raman spectroscopy and solvation measurements do not detect significant changes in the bulk electrolyte, which we attribute to the low concentration of the species, stable interfacial impacts can be observed through electrochemical impedance spectroscopy (EIS).

EASE yields statistically significant cycling performance improvements in in Li|Cu cells across different electrolytes including carbonates and fluorinated ethers. Moreover, we find improved cycling performance in Cu|LFP anode-free full cells with our additive when compared to one state-of-the-art electrolyte F5DEE. Broadly, EASE may provide new ways of functional in-situ surface modification in different battery chemistries with easy scalability.