Sandwich-type CoSe2-CNWs@rGO/S composites with efficient trapping and catalytic conversion of polysulfides in lithium-sulfur batteries.

Although lithium-sulfur batteries (LSBs) are very promising in energy storage devices, their low conductivity, shuttle effect, and volume expansion unfavorably lead to sluggish kinetics and worsening electrochemical performance. To address these problems, we firstly prepared conductive carbon nanowires embedded with lithiophilic CoSe2 nanoparticles (CoSe2-CNWs), and utilized CoSe2-CNWs to construct reduced graphene oxide (rGO) sheets; thereby, sandwich-type CoSe2-CNWs@rGO composites were assembled. CoSe2-CNWs@rGO composites were taken as the sulfur host. Due to the alternating rGO sheets and active sulfur, the special sandwich structure can maximize the use of sulfur, confine polysulfides physically, favor electron transport, and cushion the volume change during cycling. The interlayer CoSe2-CNWs network also can entrap polysulfides chemically, promote the electron transfer, and improve the reaction kinetics, owing to the synergetic merits of high polarity and conductivity. Compared with CoSe2-CNWs/S and Co-CNWs/S, the CoSe2-CNWs@rGO/S cathode shows a significant improvement in cell performance. Its specific capacity decreases from 1137.9 mA h g-1 at 0.1 C to 649.7 mA h g-1 at 2 C, demonstrating the optimal rate performance. The cycling capacity also slowly reduces from 975.4 mA h g-1 to 839.7 mA h g-1 after 150 cycles at 0.5 C, showing a high retention of 86.1% with a tiny average fading rate (0.093%).