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Optimization of lithium-sulfur batteries highly depends on exploring and characterizing new cathode materials. Sulfur/carbon copolymers have recently attracted much attention as an alternative class of cathodes to replace crystalline sulfur. In particular, poly(sulfur-n-1,3-diisopropenylbenzene) (S/DIB) has been under considerable experimental and theoretical investigations, promising a good performance in mitigating the so-called shuttle effect. Here, combining ab initio Raman spectroscopy simulations with experimental measurements, we show that S/DIB copolymers containing short and long sulfur chains are distinguishable based on their Raman activity in 400-500 1/cm. This frequency range corresponds to S--S stretching vibrations and is only observed in the Raman spectra of those copolymers with longer sulfur chains. The results reported in this study have direct applications in identification and characterization of general sulfur/carbon copolymers with different sulfur contents.

Sulfur co-polymers have recently drawn considerable attention as alternative cathode materials for lithium-sulfur batteries, thanks to their flexible atomic structure and the ability to provide high reversible capacity. Here, we report on the atomic structure of sulfur/1,3-diisopropenylbenzene co-polymers (poly(S-co-DIB)) based on the insights obtained from density-functional theory calculations. The focus is set on studying the local structural properties, namely the favorable sulfur chain length (Sn with n=1⋯8 ) connecting two DIBs. In order to investigate the effects of the organic groups and sulfur chains separately, we perform series of atomic structure optimizations. We start from simple organic groups connected via sulfur chains and gradually change the structure of the organic groups until we reach a structure in which two DIB molecules are attached via sulfur chains. Additionally, to increase the structural sampling, we perform temperature-assisted minimum-energy structure search on slightly simpler model systems. We find that in DIB-Sn -DIB co-polymers, shorter sulfur chains with n∼4 are preferred, where the stabilization is mostly brought about by the sulfur chains rather than the organic groups. The presented results, corresponding to the fully charged state of the cathode in the thermodynamic limit, have direct applications in the field of lithium-sulfur batteries with sulfur-polymer cathodes.

In this work, the photoelectron spectrum of adenine (AD) interacting with one and two bare and microhydrated Na+ (AD-Na+, Na+-AD-Na+, AD-[Na(H2O)n]+ and [Na(H2O)n]+-AD-[Na(H2O)n]+) have been calculated in two environments including the gas phase and water, separately. The symmetry adapted/cluster configuration interaction (SAC-CI) methodology was employed to calculate the first to fifth ionization energies (IEs) of AD. The photoelectron spectra of AD-Na+ structures showed a shift to higher binding energy, depending on the interaction site of Na+, compared to the spectrum of bare AD in gas phase while a slight shift to lower binding energy was observed for the spectrum of the most stable structure of AD-Na+ in water compared to bare AD in the same condition. In the presence of second Na+, the gas phase photoelectron spectrum of Na+-AD-Na+ shifted to higher binding energy compared to the spectrum of AD-Na+. This energy shift was nearly independent of the interaction site of second Na+ and decreased, considerably in the water environment. The microhydration of Na+ in the AD-Na+ and Na+-AD-Na+ structures in the gas phase, shifted their photoelectron spectra to lower binding energies compared to the spectra of corresponding unhydrated structures depending on the number of water molecules. A similar trend was also observed in water. The hydration of Na+ could decrease the ionization energy of AD-Na+ and Na+-AD-Na+ structures in water even lower than the ionization energies of bare AD in the same conditions. The main electronic configurations of the ionization bands of each structure were determined and their changing with the Na+ interaction site, number of Na+ and hydration of Na+ were explained. The kind and contribution of Lewis orbitals in the canonical molecular orbitals participating in ionization were determined for each structure.