Chitosan with abundant of hydroxyl and amine groups as an additive for cathode and separator has been proved to be an effective polysulfide trap agent in lithium-sulfur batteries. Compared with common sulfur cathode, the cathode with chitosan shows enhanced initial discharge capacity from 950 to 1145 mAh g -1 at C/10. The reversible specific capacity after 100 cycles increases from 508 mAh g -1 to 680 mAh g -1 and 473 to 646 mAh g -1 at rates of C/2 and 1C, respectively. In addition, batteries with separators that are coated with carbon/chitosan layer can exhibit high discharge capacity of 830 mAh g -1 at C/2 after 100 cycles and 675 mAh g -1 at 1C after 200 cycles with the capacity fading as low as 0.11% per cycle. These studies demonstrate the benefits of using chitosan for not only lithium-sulfur batteries but also potentially other sulfur-based battery applications.

Synthesis of a Ca(OH)2–carbon framework from crab shells and the polysulfide-trapping mechanisms of the modified separator for Li–S batteries.

The realization of a practical lithium sulfur battery system, despite its high theoretical specific capacity, is severely limited by fast capacity decay, which is mainly attributed to polysulfide dissolution and shuttle effect. To address this issue, we designed a thin cathode inactive material interlayer modified separator to block polysulfides. There are two advantages for this strategy. First, the coating material totally comes from the cathode, thus avoids the additional weights involved. Second, the cathode inactive material modified separator improve the reversible capacity and cycle performance by combining gelatin to chemically bond polysulfides and the carbon layer to physically block polysulfides. The research results confirm that with the cathode inactive material modified separator, the batteries retain a reversible capacity of 644 mAh g(-1) after 150 cycles, showing a low capacity decay of about 0.11% per circle at the rate of 0.5C.

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