Atomic-Scale Rational Designs of Superionic Sulfide-Based Solid-State Electrolytes By Atomic Layer Deposition
Authors: Meng Xiangbo , Elam Jeffrey W. 
Published: February 2020

Liquid electrolytes currently are widely utilized in lithium batteries, serving as a lithium-ion conductor but an electrical insulator. However, their flammable nature poses serious safety concerns and their reactivity to electrodes underlies performance-fading of lithium batteries. In this context, solid-state electrolytes are highly regarded as a safe and reliable alternative and undergoing intensive investigation. Traditional processes (e.g., solid-state reaction, mechanochemical method, and melt-quenching method) have enabled various superionic solid-state electrolytes, but there have been challenges to achieve intimate assembling contacts between solid-state electrolytes and electrodes. To this end, an in-situ method will be the most desirable for growing solid-state electrolytes directly on electrodes with minimal interfacial resistance. In this regard, atomic layer deposition (ALD) recently has raised an increasing interest for solid-state electrolytes, featuring its defect-free uniformity, unrivaled conformal deposition, low temperature, and rational tunability. To date, ALD has mainly reported for synthesizing oxide-based solid-state electrolytes, realizing an ionic conductivity of 2.2 x 10-6 S/cm [1] at best. Recently we conducted the first study on sulfide-based solid-state electrolytes using ALD and brought a big breakthrough for achieving superionic solid-state electrolytes. Through rationally combining two ALD processes for binary Li-S and Al-S compounds [2, 3], in the study we synthesized a series of ternary compounds of LixAlyS. Our impedance measurements revealed that the resultants LixAlyS films are promising solid-state electrolytes with tunable ionic conductivities up to over 10-3 S/cm, at least three orders of magnitude higher than those of previous oxide-based counterparts by ALD. In the study, we also characterized the composition of the resultant LixAlyS films using quartz crystal microbalance (QCM), inductively coupled plasma (ICP) mass spectrometry, and X-ray photoelectron spectroscopy (XPS). In addition, we investigated the growth of the LixAlyS films using in-situ
Fourier transform infrared spectroscopy (FTIR) and QCM. Very interestingly, we demonstrated that the resultant LixAlyS films have exceptional properties in inhibiting the growth of lithium dendrite structures in lithium batteries. Thus, this study is significant for developing all-solid-state batteries via the in-situ ALD growth of superionic solid-state electrolytes.

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