Abstract: Lithium-sulfur (Li—S) batteries using unconventional-phase transition metal dichalcogenides (TMDs), such as 1T?-WS2, as the functional layer on the separator. The unique atomic structure of 1T?-WS2 facilitates the strong immobilization and excellent catalytic ability in the conversion of polysulfide intermediates during cycling. Furthermore, the self-assembling of 1T?-WS2 greatly decreases the internal porosity, minimizing the uptake of electrolyte, which can further guarantee the performance of the battery under lean electrolyte conditions. As a result, a cell based on the 1T?-WS2 shows improved performances under high sulfur loading and lean electrolyte conditions. A cell with 12 mg cm?2 mass loading of S with only 25% oversized Li metal anode can deliver specific energy of at least 400 Wh kg?1 and 820 Wh L?1, which is among the best of reported Li—S batteries.

Abstract: A one-step salt-assisted general synthetic methodology for the controlled phase transformation of various types of 2H-phase transition metal dichalcogenides (2H-TMDs), yielding large-scale metastable 1T?-phase transition metal dichalcogenides (1T?-TMDs), including WS2, WSe2, MoS2, and MoSe2 is described. By tuning the reaction conditions, alloyed 1T?-TMDs such as WS2xSe2(1?x) and MoS2xSe2(1?x) are also obtained. Commercially-available metal salts such as K2C2O4·H2O, Na2C2O4, K2CO3, Na2CO3, Cs2CO3, Rb2CO3, KHCO3, and NaHCO3, are demonstrated to be effective for the controlled phase transformation at elevated temperatures in a reducing atmosphere. The technique may be extended to the phase engineering of other materials with various polymorphs.