The structure of sulfur-poly(acrylonitrile)-based Li-sulfur batteries is elucidated and correlated with the electrochemical performance of such devices. Apart from the poly(acrylonitrile)-derived backbone, thioamide as well as poly(sulfide) structures are proposed. Furthermore, the intermediary formation of S8 during cycling and the role of the electrolyte in its reintegration during charging into are addressed. In summary, a comprehensive picture of the chemistry and electrochemistry of Li-sulfur batteries is presented.

Starting from differently substituted boronic acids as versatile building block, new "ortho-aryl" alpha-diimine ligands a-h were synthesized in an easy, high-yielding route. Reaction of the complex precursor diacetylacetonato-nickel(II) with a trityl salt, like [CPh3] [B(C6F5)4] or [CPh3] [SbCl6], in the presence of the diimine ligands afford the monocationic, square planar complexes 2a-g in almost quantitative yields. Suitable crystals (2d',e,f,g) were submitted for X-ray diffraction analysis. A geometry model was developed to describe the orientation of ligand fragments around the nickel(II) center that influence the polymer microstructure. At elevated reaction temperature and pressure, and in the presence of hydrogen, 2a-e catalyze the homopolymerization of ethylene to give branched PE products ranging from HD- to LLD-PE grades. The polymerization results indicate the possibility of precise microstructure control depending on the particular complex substitution. Preliminary investigations on material density and mechanical behavior by uniaxial stretching until failure point toward new material properties that can result from the simple ethylene monomer by catalyst design.

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Sulfur-poly(acrylonitrile) (SPAN) composites were synthesized from different poly(acrylonitrile)- (PAN) sulfur mixtures. This way it was possible to increase the sulfur content and concomitantly the measured specific capacity of the final lithium-sulfur batteries from 300 mAh/gcathode to 440 mAh/gcathode (629 mAh/gcomposite, 1429 mAh/gsulfur). A maximum of 44 wt-% of covalently bound sulfur was reached using a PAN-sulfur ratio of 1:15 (wt/wt). Virtually no loss of capacity was observed during the first 40 cycles.

An efficient synthetic strategy for new 2,5-and 2,6-substituted unbridged and 1,4-dithiane bridged ligands is presented. The reaction of the latter compounds with Ni(acac) 2 and trityl tetrakis-(pentafluorophenyl)borate gave the corresponding Ni(II) complexes in high yields. The structure of one of these complexes was determined by X-ray analysis. These complexes were supported on silica without a chemical tether and were used as catalysts for ethylene polymerization reactions in the gas phase. Furthermore, ethylene was polymerized with the unsupported 2,5-complexes in homogeneous solution for comparison. The influence of the ligand structure, hydrogen and temperature on the polymerization performance was investigated. The supported catalysts showed moderate to high activities and produced polyethylenes ranging from HDPE to LLDPE, without further addition of an 1-olefin comonomer. In contrast to 2,6complexes, which generate high molecular weight polyethylene, the 2,5-compounds afford materials of lower molecular weight comprising terminal and internal double bonds. In addition, video microscopy experiments allowed to investigate the growth of single polyethylene particles. Electron microscopy was applied to show that their morphology is a replicate of the starting catalyst grains.Chart 1. r-Diimine Nickel(II) Complexes