Effect of molybdenum disulfide doping with substitutional nitrogen and sulfur vacancies on lithium intercalation

Abstract

Molybdenum disulfide (MoS2) nanomaterials were synthesized by rapid decomposition of ammonium tetrathiomolybdate in argon or ammonia at 600 °C and 700 °C. The change of environment had no effect on the morphology, but it affected the composition and electronic structure of the nanomaterial. The use of gaseous NH3 in the synthesis led to the incorporation of nitrogen and the formation of sulfur vacancies in the MoS2 lattice. An electrochemical study showed that this dual lattice modification significantly reduced the irreversible capacity in the first cycle and improved the lithium capacity and structural stability of MoS2 in the voltage range of 2.5–1.1 V. After 65 cycles of the operation of lithium-ion battery, the specific capacity of the defective MoS2 was 189 mAh g–1, which is higher than the theoretical capacity of ideal MoS2. An increase in electrical conductivity and a decrease in charge transfer resistance determined by using electrochemical impedance spectroscopy were associated with a decrease in the band gap in MoS2 due to the substitutional nitrogen atoms and sulfur vacancies, as shown by density functional theory calculations. In addition, these defects create new sites for lithium adsorption and increase the intercalation voltage.