Investigation of the mechanism of metal–organic frameworks preventing polysulfide shuttling from the perspective of composition and structure†
The most critical obstacle preventing lithium–sulfur batteries (LSBs) from practical application is the shuttle effect. Herein, we present a zirconium based metal–organic framework (MOF) composite separator which effectively blocks polysulfides from shuttling without hampering the migration of lithium ions owing to the sieving effect of the MOFs. Moreover, owing to the high Brunauer–Emmett–Teller (BET) surface area of 1418 m2 g−1 and chemical interactions with zirconium and oxygen on the MOFs, the polysulfides can also be physically and chemically adsorbed on the surface of the MOFs, which further blocks the polysulfides from shuttling through the intergranular channels of the MOF particles. In addition, the wettability of the composite separator with the electrolyte is enhanced owing to the polar functional groups of –COOH and –OH on the MOFs. The battery with a composite separator delivers an initial discharge capacity of 1239 mA h g−1 at 0.2C and 1147.4 mA h g−1 at 0.5C. The reversible capacity is maintained at 964.1 mA h g−1 with an average fading of only 0.08% per cycle at 0.5C. The capacity at the 2C rate with the composite separator is 955.8 mA h g−1, which is far more than that of the pristine separator, which is 289.2 mA h g−1.