Highly Rich 1T Metallic Phase of Few-Layered WS₂ Nanoflowers for Enhanced Storage of Lithium-Ion Batteries

Abstract

Transition-metal dichalcogenides (TMDs), a two-dimensional (2D) nanostructured material, has, to a greater extent, technological applications in catalysis, sensors, lithium-ion batteries, and optoelectronic devices due to their unique structure and electrical properties. Recently, the 2D TMD tungsten disulfide (WS2) has been regarded as one of the most promising anode candidates for lithium-ion batteries. However, the exploration of the WS2 sheets with the 1T metallic phase still remains a prodigious challenge to improve its conductivity and cycling stability in the application of lithium-ion batteries. In this work, the highly rich 1T few-layered WS2 nanoflowers (referred to as rich 1T WS2 NFs) were synthesized, exhibiting a rich 1T metallic phase with few-layered structures around the active edge sites of the NFs for achieving a fast electron/ion transfer, thereby delivering the enhanced cycling performance and lithium storage. The rich 1T WS2 NFs exhibits an irreversible capacity (charge capacity) of 810 mA h g–1 at 0.2 C, and after five cycles the average reversible capacity (discharge capacity) exhibits 609, 577, 554, 542, 530, and 504 mA h g–1, with the increased c-rates of 0.4, 0.6, 0.8, 1, 1.5, and 2.0 C, respectively. In addition, the rich 1T WS2 NFs anode without additional carbon support exhibits an initial capacity of 890 mA h g–1 and still remains at a capacity of 390 mA h g–1 after 500 cycles, being better than the 2H WS2 NFs and the bulk WS2 sheets. This excellent rate of performance is further attributed to the rich 1T metallic nature of the few-layered WS2 NFs that could well-promote the excellent cycling stability and rate capability in contrast to the carbon free (i.e., graphene, CNTs) composites. More importantly, the enlarged interlayer spacing (i.e., 0.67 nm) and its rich 1T metallic nature are beneficial for the high capacity and improved long cycling stability and thus makes a potential candidate for the superior Li-ion storage anodes.

Ionic Liquid‐Intercalated Metallic MoS2 as a Superior Electrode for Energy Storage Applications

“…In the 2H phase, sulfur atoms were arranged in trigonal prismatic manner around the Mo center whereas in the 1T phase one of the sulfur plane (upper or lower) in the trigonal prism rotates about 60° to obtain octahedral geometry where the Mo atom occupies the octahedral hole . Among these two phases, 1T phase exhibits superior electrochemical properties over the 2H phase . 1T‐MoS 2 comprises conducting basal planes along with the active edge sites whereas 2H‐MoS 2 is comprised of only active edges .…”

“…[14,20] Among these two phases, 1T phase exhibits superior electrochemical properties over the 2H phase. [15,[21][22] 1T-MoS 2 comprises conducting basal planes along with the active edge sites whereas 2H-MoS 2 is comprised of only active edges. [12,[23][24] However, the thermodynamically metastable nature of 1T-MoS 2 resists its usage for the energy related applications.…”

W2C/WS2 Alloy Nanoflowers as Anode Materials for Lithium-Ion Storage

“…To evaluate the electrochemical performance of the alloys for application as LIB anode materials, their CV tests were carried out for three cycles over the voltage range of 0.1–3.0 V ( Figure 5 a–d). In the first cycle, the as-prepared WS 2 NFs showed lithiation at 0.5, 1.2, and 1.4 V attributing to the reduction of WS 2 to Li 2 S through multiple steps, including the formation of Li x WS 2 and Li 2 S [ 28 ]. The peak observed at 0.5 V corresponds to the conversion reaction (4Li + + WS 2 + 4e − → 2Li 2 S + W) as well as the decomposition of the non-aqueous electrolyte to form the solid electrolyte interface (SEI) layer [ 28 , 39 ].…”

“…In the first cycle, the as-prepared WS 2 NFs showed lithiation at 0.5, 1.2, and 1.4 V attributing to the reduction of WS 2 to Li 2 S through multiple steps, including the formation of Li x WS 2 and Li 2 S [ 28 ]. The peak observed at 0.5 V corresponds to the conversion reaction (4Li + + WS 2 + 4e − → 2Li 2 S + W) as well as the decomposition of the non-aqueous electrolyte to form the solid electrolyte interface (SEI) layer [ 28 , 39 ]. In the second cycle, the peak at 0.5 V disappeared because of the formation of the SEI and gel-like polymeric layers by the dissolution of Li 2 S into the electrolyte, leading to its degradation [ 40 ].…”

“…Feng et al prepared WS 2 nanoflakes with a high reversible capacity of 680 mAh g −1 for 20 cycles as anode materials for LIBs [ 27 ]. Srinivaas et al have prepared highly rich 1T WS 2 phase in few layered nanoflowers (NFs) with stable electrochemical performance and a high initial capacity of approximately 890 mAh g −1 as anode materials for LIBs [ 28 ]. W 2 C is a good catalyst.…”