Controllable synthesis of few-layer ammoniated 1T′-phase WS2 as an anode material for lithium-ion batteries

Two-dimensional transition metal dichalcogenide (TMDC) nanosheets have received significant attention as anode materials for lithium-ion batteries, especially in their metallic 1T/1T' phase. However, controllable synthesis of few-layer 1T/1T' phase is still a challenge. In the present study, we report a facile two-step hydrothermal method to controllably synthesize few-layer 1T'-phase WS2. By tuning the redox-temperature of (NH4)2WS4 from 160 to 200 °C, the thickness of 1T'-phase WS2 can be adjusted from 4-6 to 20 layers. A higher reversible capacity is achieved in 1T'-phase WS2 with a smaller thickness, but the cycling stability decreases due to the lower crystallinity. The 1T'-phase WS2 synthesized by reduction of (NH4)2WS4 at 180 °C shows a moderate thickness of 10 layers and crystallinity, exhibiting the optimal Li-ion storage properties, i.e. a reversible capacity of 855.9 mA h g-1 at 100 mA g-1 and a good rate performance of 354.4 mA h g-1 at 5000 mA g-1. These results provide new insights into understanding the impacts of layer number on the Li-ion storage properties of 1T'-phase WS2.