Studies on the inhibition of lithium dendrite formation in sulfide solid electrolytes doped with LiX (X = Br, I)

A promising method to increase the energy density of all-solid-state batteries (ASSBs) featuring lithium ions as carriers is to employ Li metal as the anode. However, this has been accompanied by safety problems like flammable accidents associated with lithium dendrites originating from reactions with the solid electrolyte, leading to reduced battery performance. To overcome this issue toward the commercialization of ASSBs, various approaches have been proposed by many researchers. Among the suggested solutions, the use of lithium-halide-doped Li₃PS₄, to suppress lithium dendrite formation, has attracted attention. LiI-doped Li₃PS₄ has shown the highest lithium dendrite growth suppression among lithium-halide-doped systems, but the reason for this is unclear. Thus, we attempted to clarify the cause of this suppression by comparing LiBr-doped Li₃PS₄ with LiI-doped Li₃PS₄. Investigation using various methods such as electrochemical evaluation, X-ray absorption spectroscopy, X-ray computed tomography, and pair distribution function analysis revealed that two factors affect the suppression of Li dendrite growth: the suppression of the current density distribution by improving the ionic conductivity and the stable interfacial layer. This is the main reason LiI-doped Li₃PS₄ shows excellent Li dendrite suppression.