Synthesis and characterization of low-temperature lithium-ion conductive phase of LiX (X=Cl, Br)-Li3PS4 solid electrolytes

A new class of sulfide electrolytes, (1-x)LiCl-xLiBr-2Li 3 PS 4 (x = 0, 0.25, 0.50, 0.75, and 1.0), was synthesized, and characterized their stable temperature range, ionic-conductivity and applicability for all-solid-state lithium metal battery. The optimal heat-treatment temperature of the synthesis process is relatively low, i.e., 200 °C. Ionic conductivity of the electrolyte increases with increasing LiBr ratio, and maximum ionic conductivity at 25 °C is 1.7 mScm −1 with x = 0.75. At higher heat-treatment temperature, above 250 °C, a low-ionic-conduction crystalline phase appears in the electrolyte, and at that time, ionic conductivity decreases to a similar value to that of the amorphous precursor used in the synthesis process. Since the electrolyte does not contain a transition metal, it is applicable to the lithium-metal secondary system. A reversible lithium deposition-stripping reaction was demonstrated by cyclic voltammogram, the results of which indicate that the electrolyte is applicable to a typical 4-V rechargeable lithium-metal secondary system. The Coulombic efficiency of the first charge-discharge cycle is approximately 75%, and reversible capacity of 185 mAhg −1 was verified by a Li/0.25LiCl-0.75LiBr-2Li 3 PS 4 /NCA pelletized-cell test. It is concluded from these results that the proposed low-temperature-synthesized sulfide electrolytes will reduce energy consumption for material production, and such a low-carbon-footprint process meets the demand of the future sustainable society. • A new class of LiX (X = Cl, Br)-Li 3 PS 4 solid electrolytes are synthesized by using conventional solid reaction process. • 0.25LiCl-0.75LiBr-2Li 3 PS 4 solid electrolyte shows a high Li + conductivity of 1.7mScm −1 at 25 °C. • All-solid-state cells exhibits a discharge capacity of 185 mAhg −1 -NCA at 25 °C.