Li(metal)–sulfur (Li–S) systems are among the rechargeable batteries of the highest possible energy density due to the high capacity of both electrodes. The surface chemistry developed on Li electrodes in electrolyte solutions for Li–S batteries was rigorously studied using Fourier transform infrared and X-ray photoelectron spectroscopies. A special methodology was developed for handling the highly reactive Li samples. It was possible to analyze the contribution of solvents such as 1-3 dioxolane, the electrolyte LiN(SnormalO2CnormalF3)2 , polysulfide (normalLi2normalSn) , and LiNnormalO3 additives to protective surface films that are formed on the Li electrodes. The role of LiNnormalO3 as a critical component whose presence in solutions prevents a shuttle mechanism that limits the capacity of the sulfur electrodes is discussed and explained herein.

Electrolyte solutions for rechargeable Mg batteries were developed, based on reaction products of phenyl magnesium chloride ͑PhMgCl͒ Lewis base and AlCl 3 Lewis acid in ethers. The transmetallation of these ligands forms solutions with Mg x Cl y + and AlCl 4−n Ph n − ions as the major ionic species, as analyzed by multinuclei nuclear magnetic resonance spectroscopy. Tetrahydrofuran ͑THF͒ solutions of ͑PhMgCl͒ 2 -AlCl 3 exhibit optimal properties: highly reversible Mg deposition ͑100% cycling efficiency͒ with low overvoltage: Ͻ0.2 V and electrochemical windows wider than 3 V. A specific conductivity of 2-5 ϫ 10 −3 ⍀ −1 cm −1 could be measured between −10 and 30°C for these solutions, similar to that of standard electrolyte solutions for Li batteries. Mg ions intercalate reversibly with Chevrel phase ͑Mg x Mo 6 S 8 ͒ cathodes in these solutions. These systems exhibit high thermal stability. The solutions may enable the use of high voltage, high-capacity Mg insertion materials as cathodes and hence open the door for research and development of high-energy density, rechargeable Mg batteries.

The manipulation of the bandgap of graphene by various means has stirred great interest for potential applications. Here we show that treatment of graphene with xenon difluoride produces a partially fluorinated graphene (fluorographene) with covalent C-F bonding and local sp(3)-carbon hybridization. The material was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, electron energy loss spectroscopy, photoluminescence spectroscopy, and near edge X-ray absorption spectroscopy. These results confirm the structural features of the fluorographane with a bandgap of 3.8 eV, close to that calculated for fluorinated single layer graphene, (CF)(n). The material luminesces broadly in the UV and visible light regions, and has optical properties resembling diamond, with both excitonic and direct optical absorption and emission features. These results suggest the use of fluorographane as a new, readily prepared material for electronic, optoelectronic applications, and energy harvesting applications.

The interaction of Li(+) with single and few layer graphene is reported. In situ Raman spectra were collected during the electrochemical lithiation of the single- and few-layer graphene. While the interaction of lithium with few layer graphene seems to resemble that of graphite, single layer graphene behaves very differently. The amount of lithium absorbed on single layer graphene seems to be greatly reduced due to repulsion forces between Li(+) at both sides of the graphene layer.

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The electrical conductivity and the impedance behavior of thin layers of amorphous silicon (a-Si), which are promising anode materials for lithium-ion batteries, were monitored in situ during the insertion/extraction of lithium in 1 M of a LiBOB (Li-bioxalato borate) propylene carbonate solution. In addition, Raman spectra of the same electrodes were recorded in situ and ex situ during lithiation/delithiation processes in the above-mentioned solutions. The conductivity of the a-Si electrode was increased by about 3.5 orders of magnitude during the course of lithium insertion. While the impedance response of these electrodes is complicated and cannot be resolved unambiguously, it is clear that the electrical conductivity influences strongly the electrodes' impedance:  a similar dependence of the electrical conductivity and the impedance of these electrodes on the potential are measured. The intensity of the Raman signal dropped significantly upon lithiation and recovered at a potential of 0.523 V vs Li/Li+. It is suggested that the drop in the intensity of the Raman signal of the silicon electrodes upon their lithiation is due to changes in the optical skin depth of the a-Si, which occur upon the formation of the Li−Si alloy.

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