Essential Contribution of Li + Intercalation/Deintercalation Afforded by the First Layer of Coaxial Coated MoS 2 Sheets on Carbon Nanotubes

Although the combined use of MoS 2 and carbon nanotubes (CNTs) has been known to work as superior anodes for Li + intercalation/deintercalation, the essential contribution was still blurred provided by the so-called synergistic effects. To make this question clearer, we fabricated coaxial coated CNTs by MoS 2 of single- and multiple-layered sheets via a solution-based method implemented by ultrasonic agitation and co-use of the nonionic surfactant polyethylene glycol (PEG400). The synthetic conditions were found as concentrations >2.0 M of the precursor (NH 4 ) 2 MoS 4, a lower ultrasonic power (750 mA·h·g –1 for at least 100 cycles, and no decaying of Li + intercalation/deintercalation capacity was observed. The multi MoS 2 @CNTs delivered a higher capacity (∼1050 mA·h·g –1 ) but suffered from a gradual fading in Li + storage/release capacity. DFT calculations demonstrated that the typical Li + diffusion energy barrier (0.5 eV) from Oh to Th sites between two sheets of MoS 2 constructed in the multi MoS 2 @CNTs was greatly decreased to 0.20 eV for lithium transfer from H to T sites between the MoS 2 sheet and the CNT surface which was constructed in mono MoS 2 @CNTs. The superior cyclability and high rate of lithiation for the hybrid of MoS 2 @CNTs were confirmed to stem mainly from the first layer of MoS 2 that was conjugated with the sp 2 surface of graphene.