The sulfide solid electrolyte synthesized via carbothermal reduction of lithium sulfate for solid-state lithium-sulfur batteries

Lithium sulfide (Li₂S) is an important and expensive reagent extensively used for the lithium–sulfur (Li–S) electrochemical systems. Especially, it is a basic reagent for the sulfide solid electrolyte synthesis. This contribution describes the development and adaptation of the synthesis of Li₂S via carbothermal reduction of lithium sulfate (Li₂SO₄). The molar ratio of the starting reagents varies from 1:4.4 to 1:2 to determine the optimal conditions by analyzing all products and their compositions. The optimal molar ratio of Li₂SO₄:C for producing Li₂S with a purity greater than 90 wt% and minimal impurities is found to be between 1:2 and 1:3. The influence of the impurities in Li₂S on the resulting sulfide solid electrolytes is evaluated by synthesizing 75Li₂S-25P₂S₅ electrolyte. The ionic conductivity of the as-obtained electrolyte is 3.3 × 10⁻³ S cm⁻¹. The presence of the impurities in the starting reagent does not influence the performance of the synthesized sulfide solid electrolyte.