Figs. 1a,b illustrate the nanocapsule structure of Li2S@graphene. TEM images show that the particles have a compact core-shell shape, where the crystalline Li2S cores display highly ordered lattice fringes, and they are surrounded by a contour coating of ~ 10 to 20 graphene layers, thus forming a capsule-like nanostructure. Figs. 1c-f show the electrochemical performance of Li2S@graphene composite. Even at a high electrode loading of 10 mgLi2S cm−2, the cell delivers a high initial charge capacity of 1600 mAh g−1 and a high discharge capacity of 1160 mAh g−1. The capacity remains at 600 mAh g−1 after 200 cycles. In addition, the cell exhibits a good rate capability with high discharge capacities of 1230 (0.1 C), 1105 (0.2 C), 984 (0.5 C), 802 (1.0 C), and 600 mAh g−1 (2.0 C). This finding is mainly attributed to the improved electrical properties, electrochemical kinetics, and structural stability of Li2S@graphene nanocapsules. In a word, this compact Li2S@graphene capsule nanostructure exhibit good electrochemical performance.
Fig. 1 Structural and electrochemical characterization of Li2S@graphene nanocomposite. (a) TEM images of Li2S@graphene nanocapsules. (b) Schematic showing the compact nanocapsule structure. (c) Voltage profiles and (d) Cycling performance of Li2S@graphene electrode based on electrode loading of 10 mgLi2S cm−2. (e) Voltage profiles at different charge/discharge current densities, and (f) Long rate cycling performance of Li2S@graphene electrode based on electrode loading of 5 mgLi2S cm−2.