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. •The structural properties and ability to lithium dendrite suppression of LiBr–doped Li3PS4 were investigated by pair distribution function (PDF) analysis and critical current density (CCD) test in relation to the ionic conductivity.•The PDF analysis revealed that the LiBr–doped Li3PS4 solid electrolyte has a structure in which bromine is inserted between the PS43− anions.•Although Interfacial layer between LiBr-doped Li3PS4 and Li metal is stable, the interfacial resistance is relatively high.