Copolymerization of Polythiophene and Sulfur To Improve
the Electrochemical Performance in Lithium–Sulfur Batteries
- Publication date
- Publisher
Abstract
We
first report on the copolymerization of sulfur and allyl-terminated
poly(3-hexylthiophene-2,5-diyl) (P3HT) derived by Grignard metathesis
polymerization. This copolymerization is enabled by the conversion
of sulfur radicals formed by thermolytic cleavage of S<sub>8</sub> rings with allyl end-group. The formation of a C–S bond in
the copolymer is characterized by a variety of methods, including
NMR spectroscopy, size exclusion chromatography, and near-edge X-ray
absorption fine spectroscopy. The <b>S-P3HT</b> copolymer is
applied as an additive to sulfur as cathode material in lithium–sulfur
batteries and compared to the use of a simple mixture of sulfur and
P3HT, in which sulfur and P3HT were not covalently linked. While P3HT
is incompatible with elementary sulfur, the new <b>S-P3HT</b> copolymer can be well dispersed in sulfur, at least on the sub-micrometer
level. Sulfur batteries containing the <b>S-P3HT</b> copolymer
exhibit an enhanced battery performance with respect to the cycling
performance at 0.5C (799 mAh g<sup>–1</sup> after 100 cycles
for <b>S-P3HT</b> copolymer versus only 544 mAh g<sup>–1</sup> for the simple mixture) and the C-rate performance. This is attributed
to the attractive interaction between polysulfides and P3HT hindering
the dissolution of polysulfides and the charge transfer (proven by
electrochemical impedance spectroscopy) due to the homogeneous incorporation
of P3HT into sulfur by covalently linking sulfur and P3HT