Environmental and Thermal Stability of Chemically Exfoliated Li_xMoS₂ for Lithium–Sulfur Batteries

Abstract

Molybdenum disulfide (MoS 2 ) can exist in the semiconducting (2H) or metallic (1T) phase. The metallic 1T phase of MoS 2 is achieved by lithium intercalation using n-butyllithium. The resulting 1T MoS 2 can be in a lithiated form (Li x MoS 2 ) or as pure MoS 2 . The 1T phase of MoS 2 is metastable and relaxes to the stable 2H phase upon heating. Here we study the thermal and environmental stabilities of metallic phase Li x MoS 2 and pure 1T phase MoS 2 for comparison. We find that the thermal stability of 1T MoS 2 is enhanced by lithiation so that Li x MoS 2 is phase stable up to 400 °C in argon, while nonlithiated MoS 2 relaxes to the 2H phase above 150 °C. The stability of the Li x MoS 2 was monitored under ambient conditions (23 °C, 50% relative humidity). We find that the Li x MoS 2 phase progressively oxidizes up to 48 h of exposure in the ambient after which further oxidation ceases. X-ray diffraction shows that oxidation occurs via loss of sulfur and the formation of lithium molybdate (Li 2 MoO 4 ). Our analysis reveals that moisture is the primary cause of oxidation and that the 1T phase and chemistry of Li x MoS 2 can be preserved in a dry oxygen-rich environment at up to 250 °C. This enhanced stability allows the use of a conventional molten diffusion method for cathode preparation for lithium−sulfur batteries.

Quasi-Solid-State Electrolyte Induced by Metallic MoS2 for Lithium–Sulfur Batteries

“…2H MoS 2 powder (Alfa Aesar) was used as purchased without further modification. 1T MoS 2 was synthesized by chemical exfoliation of bulk 2H MoS 2 with organolithium as reported previously. ,, Briefly, bulk 2H MoS 2 powder (0.3 g) was first immersed in hexane (15 mL; Sigma-Aldrich), followed by adding n -butyllithium solution (1.6 M in hexane, 3 mL; Sigma-Aldrich) and refluxing for 2 days under argon protection. The product was then washed with hexane (50 mL) 3 times and dispersed in deionized water (1 mg mL –1 ) with the aid of ultrasonication (20 min).…”