Atomic-Scale Rational Designs of Superionic Sulfide-Based Solid-State Electrolytes By Atomic Layer Deposition

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 Li x Al y S. Our impedance measurements revealed that the resultants Li x Al y S 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 Li x Al y S 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 Li x Al y S films using in-situ Fourier transform infrared spectroscopy (FTIR) and QCM. Very interestingly, we demonstrated that the resultant Li x Al y S 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. Kazyak, E., et al., Atomic layer deposition and first principles modeling of glassy Li 3 BO 3 –Li 2 CO 3 electrolytes for solid-state Li metal batteries. Journal of Materials Chemistry A, 2018. 6 (40): p. 19425-19437. Meng, X., et al., Vapor-phase atomic-controllable growth of amorphous Li 2 S for high-performance lithium–sulfur batteries. ACS Nano, 2014. 8 (10): p. 10963-10972. Meng, X., et al., Atomic layer deposition of aluminum sulfide: growth mechanism and electrochemical evaluation in lithium-ion batteries. Chemistry of Materials, 2017. 29 (21): p. 9043-9052.