In Situ Growth of W2C/WS2 with Carbon-Nanotube Networks for Lithium-Ion Storage

Abstract

The combination of W2C and WS2 has emerged as a promising anode material for lithium-ion batteries. W2C possesses high conductivity but the W2C/WS2-alloy nanoflowers show unstable performance because of the lack of contact with the leaves of the nanoflower. In this study, carbon nanotubes (CNTs) were employed as conductive networks for in situ growth of W2C/WS2 alloys. The analysis of X-ray diffraction patterns and scanning/transmission electron microscopy showed that the presence of CNTs affected the growth of the alloys, encouraging the formation of a stacking layer with a lattice spacing of ~7.2 Å. Therefore, this self-adjustment in the structure facilitated the insertion/desertion of lithium ions into the active materials. The bare W2C/WS2-alloy anode showed inferior performance, with a capacity retention of ~300 mAh g−1 after 100 cycles. In contrast, the WCNT01 anode delivered a highly stable capacity of ~650 mAh g−1 after 100 cycles. The calculation based on impedance spectra suggested that the presence of CNTs improved the lithium-ion diffusion coefficient to 50 times that of bare nanoflowers. These results suggest the effectiveness of small quantities of CNTs on the in situ growth of sulfides/carbide alloys: CNTs create networks for the insertion/desertion of lithium ions and improve the cyclic performance of metal-sulfide-based lithium-ion batteries.