01 Basic Properties
– Chemical Properties: Lithium sulfide (Li₂S) is extremely reactive. It hydrolyzes in air to produce highly toxic hydrogen sulfide gas and cannot exist in nature. When heated to about 300°C in air, it oxidizes to lithium sulfate.
– Physical Properties: It appears as white to yellow crystals with an anti-fluorite structure, belonging to the cubic crystal system. It dissolves in water and ethanol, slightly in acid, but not in alkali. It has a melting point of 938°C, boiling point of 1,372°C, and density of 1.66g/mL.
02 Application Fields
– Battery Sector:
– As a lithium-sulfur battery cathode material, Li₂S boasts a theoretical capacity of 1,166mAh/g, nearly four times that of lithium cobalt oxide, showing great potential. Enhancing its particle size, morphology, and compounding it with conductive carbon materials or doping with nonmetallic atoms can boost battery performance.
– Solid-State Electrolytes: Li₂S is crucial for synthesizing Li₂S-P₂S₅ solid electrolytes, improving safety, cycle life, and charge/discharge efficiency of all-solid-state lithium-ion batteries, promising for electric vehicles and portable electronics.
Chemical Synthesis: Li₂S is a precursor for lithium compounds like lithium thioacetate, lithium tetrafluoroborate, and thio-LISICON, used in lithium-ion batteries. In chemical manufacturing, it produces compounds like lithium hydride, lithium borohydride, and lithium amide.
Semiconductor Industry: Li₂S is a precursor for thin-film transistors (TFTs) and electronic devices, especially Li₂S-P₂O₅ TFTs.
03 Industrial Synthesis Methods
Ball Milling: Mix sulfur and lithium/hydride in an inert atmosphere, then ball mill. Simple and eco-friendly, but costly, time-consuming, low yield, impure products, and challenging to scale up.
Solvent Method: React lithium compounds with sulfur compounds in a solvent (organic or liquid ammonia). Complete liquid-phase reactions ensure high purity and easy purification. However, organic solvents pose explosion and pollution risks.
Thermal Reduction: React Li₂S precursors with carbon-based reductants at high temperatures. Easily operated with convenient intermediate storage. Yet, it’s energy-intensive and CO₂-emitting.
Direct Carbon Composite: Add carbon materials or precursors during synthesis to produce Li₂S/carbon composites. This improves control and performance, reduces production complexity, and enhances lithium-sulfur battery electrochemical performance. But the technology needs refining, with unstable quality and poor morphology control.
04 Storage and Safety
-Storage: Store at 2–8°C in a dry, sealed environment, preferably under dry inert gas.
Safety: Use protective gear to avoid skin/eye contact and dust inhalation. Prevent acid contact to avoid toxic gas release.
Leakage: Use a respirator, ensure ventilation, and prevent dust. Collect and dispose of the product in sealed containers.
Firefighting: Extinguish with CO₂, sand, or powder, not water, to avoid toxic gas release from thermal decomposition.
