(Keynote) In-Situ Synthesis of Compact Li2s@Graphene Nanocapsules for High Performance Li-S Batteries

Wednesday, 4 October 2017: 14:40
Chesapeake K (Gaylord National Resort and Convention Center)
G. Tan, R. Xu (Argonne National Laboratory), Z. Xing (Oregon State University), Y. Yuan, J. Wen (Argonne National Laboratory), C. Liu (Argonne National Lab), L. Ma, T. Wu, J. Lu (Argonne National Laboratory), X. Ji (Oregon State University), and K. Amine (Argonne National Laboratory)
For the practical applications of Li-S batteries, excellent energy/power densities and long cycling lifetimes along with high electrode mass loading must be achieved. This requires rational design of cathode’s architectures to facilitate fast electronic and ionic transport as well as accommodate the electrode’s volumetric change. Here we report a compact Li2S/graphene cathode architectural design, where crystalline Li2S nanoparticles wrapped by graphenes are generated simultaneously by burning lithium foil in CS2 vapor, thus forming Li2S@graphene nanocapsules. This structure represents the high possible volumetric efficiency for accommodating sulfur active species while providing superior electrical properties. As a result, the composite electrode exhibits remarkable electrochemical properties, where at a mass loading of 10 mg cm−2, the electrode delivers high reversible capacity of 1160 mAh g−1S at 0.1 C rate and 800 mAh g−1S at 1.0 C rate as well as stable cycle performance.

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.