Copolymerization of Polythiophene and Sulfur To Improve the Electrochemical Performance in Lithium–Sulfur Batteries

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 S₈ 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^–1 after 100 cycles for <b>S-P3HT</b> copolymer versus only 544 mAh g^–1 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

Conformal Polymeric Multilayer Coatings on Sulfur Cathodes via the Layer-by-Layer Deposition for High Capacity Retention in Li–S Batteries

We report on the conformal coating of thickness-tunable multilayers directly onto the sulfur (S₈) cathodes by the layer-by-layer (LbL) deposition for the significant improvement in the performances of Li–S batteries even without key additives (LiNO₃) in the electrolyte. Poly­(ethylene oxide) (PEO)/poly­(acrylic acid) (PAA) multilayers on a single poly­(allylamine hydrochloride) (PAH)/PAA priming bilayer, deposited on the S₈ cathodes, effectively protected from the polysulfide leakage, while providing a Li⁺ ion diffusion channel. As a result, PAH/PAA/(PEO/PAA)₃ multilayer-coated cathodes exhibited the highest capacity retention (806 mAh g^–1) after 100 cycles at 0.5 C, as well as the high C-rate capability up to 2.0 C. Furthermore, the multilayer coating effectively mitigated the polysulfide shuttle effect in the absent of LiNO₃ additives in the electrolyte

Inverse Vulcanization of Elemental Sulfur to Prepare Polymeric Electrode Materials for Li–S Batteries

Sulfur-rich copolymers based on poly­(sulfur-<i>random-</i>1,3-diisopropenylbenzene) (poly­(S-<i>r</i>-DIB)) were synthesized via inverse vulcanization to create cathode materials for lithium–sulfur battery applications. These materials exhibit enhanced capacity retention (1005 mAh/g at 100 cycles) and battery lifetimes over 500 cycles at a C/10 rate. These poly­(S-<i>r</i>-DIB) copolymers represent a new class of polymeric electrode materials that exhibit one of the highest charge capacities reported, particularly after extended charge–discharge cycling in Li–S batteries

Elemental Sulfur and Molybdenum Disulfide Composites for Li–S Batteries with Long Cycle Life and High-Rate Capability

The practical implementation of Li–S technology has been hindered by short cycle life and poor rate capability owing to deleterious effects resulting from the varied solubilities of different Li polysulfide redox products. Here, we report the preparation and utilization of composites with a sulfur-rich matrix and molybdenum disulfide (MoS₂) particulate inclusions as Li–S cathode materials with the capability to mitigate the dissolution of the Li polysulfide redox products via the MoS₂ inclusions acting as “polysulfide anchors”. In situ composite formation was completed via a facile, one-pot method with commercially available starting materials. The composites were afforded by first dispersing MoS₂ directly in liquid elemental sulfur (S₈) with sequential polymerization of the sulfur phase via thermal ring opening polymerization or copolymerization via inverse vulcanization. For the practical utility of this system to be highlighted, it was demonstrated that the composite formation methodology was amenable to larger scale processes with composites easily prepared in 100 g batches. Cathodes fabricated with the high sulfur content composites as the active material afforded Li–S cells that exhibited extended cycle lifetimes of up to 1000 cycles with low capacity decay (0.07% per cycle) and demonstrated exceptional rate capability with the delivery of reversible capacity up to 500 mAh/g at 5 C

Elemental Sulfur and Molybdenum Disulfide Composites for Li–S Batteries with Long Cycle Life and High-Rate Capability

The practical implementation of Li–S technology has been hindered by short cycle life and poor rate capability owing to deleterious effects resulting from the varied solubilities of different Li polysulfide redox products. Here, we report the preparation and utilization of composites with a sulfur-rich matrix and molybdenum disulfide (MoS₂) particulate inclusions as Li–S cathode materials with the capability to mitigate the dissolution of the Li polysulfide redox products via the MoS₂ inclusions acting as “polysulfide anchors”. In situ composite formation was completed via a facile, one-pot method with commercially available starting materials. The composites were afforded by first dispersing MoS₂ directly in liquid elemental sulfur (S₈) with sequential polymerization of the sulfur phase via thermal ring opening polymerization or copolymerization via inverse vulcanization. For the practical utility of this system to be highlighted, it was demonstrated that the composite formation methodology was amenable to larger scale processes with composites easily prepared in 100 g batches. Cathodes fabricated with the high sulfur content composites as the active material afforded Li–S cells that exhibited extended cycle lifetimes of up to 1000 cycles with low capacity decay (0.07% per cycle) and demonstrated exceptional rate capability with the delivery of reversible capacity up to 500 mAh/g at 5 C