Abstract
Lithium sulfide (Li2S) is under intense study because it is the insulating discharge product of ultra-high energy density lithium-sulfur (Li-S) batteries and a candidate cathode material for lithium metal-free Li-S cells. In this work, we report the fabrication of an apparatus for sputter deposition of Li2S films ranging in thickness from a few nanometers to several microns at rates over 2 nm min-1. High-temperature annealing of the films is shown to produce crystalline films of high chemical purity Li2S for the first time. We provide evidence that sputter deposition produces a unique sulfide structure composed of chains of Li2S units, and that the electrochemistry of these films is markedly different from annealed crystalline Li2S, which is shown to be electrochemically inactive. Finally, we explore trends in the plasma chemistry that lead to nonstoichiometry and depth inhomogeneity during Li2S sputter deposition.
