context: The comprehensive electrochemical and theoretical investigations suggested that the MoS2 NDs with strong LPS absorptivity and high catalytic property would be an ideal choice for robust electrochemical performance for LSBs. Thus, we systematically performed electrochemical measurements of MoS2 ND/porous carbon/Li2S6, in comparison with porous carbon/Li2S6 and MoS2 sheet/porous carbon/Li2S6 cathodes. Fig. 6a shows the CV curves of MoS2 ND/porous carbon/Li2S6 between 1.7–2.8 V vs. Li+/Li at a scan rate of 0.1 mV s−1. Two cathodic peaks at 2.26 and 2.01 V were delivered during the first scan, which were assigned to the reduction of long-chain polysulfides to short-chain Li2S4 and further to solid Li2S. The reversible oxidation of Li2S to polysulfides and to sulfur were presented by two anodic peaks at 2.39 and 2.47 V, respectively. In the following three cycles, the overlap of the discharge/charge peaks evidently indicated the excellent reversibility of the MoS2 ND/porous carbon/Li2S6 electrode. Note that a slight negative shift of the cathodic peak from 2.26 V in the 1st sweep to 2.28 V in the following sweeps could be observed, possibly due to the increased polarization as the starting material changed from a liquid catholyte to solid sulfur from the 2nd cycle. The excellent reversibility was also confirmed by discharging/charging at 0.1C for 100 cycles (Fig. 6b). The MoS2 ND/porous carbon/Li2S6 electrode presented a capacity of 1107 mA h g−1 at the 2nd cycle and retained 1020 mA h g−1 after 100 cycles, rendering a low capacity degradation rate of 0.08% per cycle. In contrast, the porous carbon/Li2S6 and MoS2 sheet/porous carbon/Li2S6 presented much higher capacity fading rates of 0.5% and 0.19% per cycle, respectively (Fig. S11, ESI†).
answer: carbon/Li2S6