Accelerated Reversible Conversion of Li2S2 to Li2S by Spidroin Regulated Li+ Flux for High-performance Li-Sulfur Batteries.

Regulating the transformation of sulfur species is the key to improving the electrochemical performance of lithium-sulfur (Li-S) batteries, in particular, to accelerate the reversible conversion between solid phase Li2S2 and Li2S. Herein, we introduced Spidroin, which is a main protein in spider silk, as a dual functional separator coating in Li-S batteries to effectively adsorb polysulfides via the sequence of amino acids in its primary structure and regulate Li+ flux through the ß-sheet of its secondary structure, thus accelerating the reversible transformation between Li2S2 and Li2S. Spidroin-based Li-S cells exhibited an exceptional electrochemical performance with a high specific capacity of  744.1 mAh g-1 at 5C and a high areal capacity of 7.5 mAh cm-2 at a low electrolyte-to-sulfur (E/S) ratio of 6 µL mgs-1 and a sulfur loading of 8.6 mgs cm-2.

High Crystallinity 2D π-d Conjugated Conductive Metal-Organic Framework for Boosting Polysulfide Conversion in Lithium-Sulfur Batteries.

The catalytic performance of metal-organic frameworks (MOFs) in Li-S batteries is significantly hindered by unsuitable pore size, low conductivity, and large steric contact hindrance between the catalytic site and lithium polysulfide (LPSs). Herein, the smallest π-conjugated hexaaminobenzene (HAB) as linker and Ni(II) ions as skeletal node are in situ assembled into high crystallinity Ni-HAB 2D conductive MOFs with dense Ni-N4 units via dsp2 hybridization on the surface of carbon nanotube (CNT), fabricating Ni-HAB@CNT as separator modified layer in Li-S batteries. As-obtained unique π-d conjugated Ni-HAB nanostructure features ordered micropores with suitable pore size (≈8 Å) induced by HAB ligands, which can cooperate with dense Ni-N4 chemisorption sites to effectively suppress the shuttle effect. Meanwhile, the conversion kinetics of LPSs is significantly accelerated owing to the small steric contact hindrance and increased delocalized electron density endued by the planar tetracoordinate structure. Consequently, the Li-S battery with Ni-HAB@CNT modified separator achieves an areal capacity of 6.29 mAh cm-2 at high sulfur loading of 6.5 mg cm-2 under electrolyte/sulfur ratio of 5 µL mg-1 . Moreover, Li-S single-electrode pouch cells with modified separators deliver a high reversible capacity of 791 mAh g-1 after 50 cycles at 0.1 C with electrolyte/sulfur ratio of 6 µL mg-1 .