Batteries based on sodium superoxide and on potassium superoxide have recently been reported. However, there have been no reports of a battery based on lithium superoxide (LiO2), despite much research into the lithium-oxygen (Li-O2) battery because of its potential high energy density. Several studies of Li-O2 batteries have found evidence of LiO2 being formed as one component of the discharge product along with lithium peroxide (Li2O2). In addition, theoretical calculations have indicated that some forms of LiO2 may have a long lifetime. These studies also suggest that it might be possible to form LiO2 alone for use in a battery. However, solid LiO2 has been difficult to synthesize in pure form because it is thermodynamically unstable with respect to disproportionation, giving Li2O2 (refs 19, 20). Here we show that crystalline LiO2 can be stabilized in a Li-O2 battery by using a suitable graphene-based cathode. Various characterization techniques reveal no evidence for the presence of Li2O2. A novel templating growth mechanism involving the use of iridium nanoparticles on the cathode surface may be responsible for the growth of crystalline LiO2. Our results demonstrate that the LiO2 formed in the Li-O2 battery is stable enough for the battery to be repeatedly charged and discharged with a very low charge potential (about 3.2 volts). We anticipate that this discovery will lead to methods of synthesizing and stabilizing LiO2, which could open the way to high-energy-density batteries based on LiO2 as well as to other possible uses of this compound, such as oxygen storage.

Three-dimensional topological Dirac semimetals have a linear dispersion in 3D momentum space and are viewed as the 3D analogues of graphene. Here, we report angle-dependent magnetotransport on the newly revealed Cd 3 As 2 single crystals and clearly show how the Fermi surface evolves with crystallographic orientations. Remarkably, when the magnetic field lies in the [112] or ½441 axis, magnetoresistance oscillations with only single period are present. However, the oscillation shows double periods when the field is applied along the ½110 direction. Moreover, aligning the magnetic field at certain directions also gives rise to double period oscillations. We attribute the observed anomalous oscillation behavior to the sophisticated geometry of Fermi surface and illustrate a complete 3D Fermi surface with two nested anisotropic ellipsoids around the Dirac points. Additionally, a submillimeter mean-free path at 6 K is found in Cd 3 As 2 crystals, indicating ballistic transport in this material. By measuring the magnetoresistance up to 60 T, we reach the quantum limit (n ¼ 1 Landau level) at about 43 T. These results improve the knowledge of the Dirac semimetal material Cd 3 As 2 and also pave the way for proposing new electronic applications based on 3D Dirac materials.

The synthesis and X-ray characterization of two new dialkynylated diazatetracenes and the corresponding N, N-dihydrodiazatetracenes are reported. The dialkynylated heteroacenes are packed in a brick-wall motif that enforces significant overlap of their pi-faces. Cyclic voltammetry indicates that the dehydrogenated forms are easily reduced to their radical anions in solution. The planarity of these species validates the discussion of their aromaticity. Nucleus Independent Chemical Shift (NICS) computations demonstrate that both of these 20 pi and 24 pi electron systems are aromatic. Both experimental and computational results suggest that the aromaticity of the dihydroheteroacenes is reduced.

Large acenes, particularly pentacenes, are important in organic electronics applications such as thin-film transistors. Derivatives where CH units are substituted by sp 2 nitrogen atoms are rare but of potential interest as charge-transport materials. In this article, we show that pyrazine units embedded in tetracenes and pentacenes allow for additional electronegative substituents to induce unexpected redshifts in the optical transitions of diazaacenes. The presence of the pyrazine group is critical for this effect. The decrease in transition energy in the halogenated diazaacenes is due to a disproportionate lack of stabilization of the Homo on halogen substitution. The effect results from the unsymmetrical distribution of the Homo, which shows decreased orbital coefficients on the ring bearing chlorine substituents. The more strongly electron-accepting cyano group is predicted to shift the transitions of diazaacenes even further to the red. Electronegative substitution impacts the electronic properties of diazaacenes to a much greater degree than expected.

Enlarged acenothiadiazoles, which are easily prepared, display attractive optical and electrochemical properties. The annulation of thiadiazole to anthracene gives a stable material with optical properties similar to those of substituted pentacenes.

[reaction: see text] A shape-persistent, conjugated o-phenylene ethynylene cyclic trimer was prepared in one step from tetrasubstituted benzene monomer 4 in 86% isolated yield through precipitation-driven alkyne metathesis. The template-free, selective generation of the molecular triangle 5 is a thermodynamically favored process and under equilibrium control. A novel tetrameric macrocycle 7 was generated via scrambling metathesis between tricycle 5 and hexacycle 6 using this dynamic covalent chemistry.

The effect of MgCl 2 on a series of chloride containing magnesium electrolytes was investigated. In the presence of extra MgCl 2 , the electrochemical properties of Grignard reagents (RMgCl, R = Ph, Et, i Pr) were significantly improved, and the advantage of MgCl 2 was further demonstrated in Mg-Mo 6 S 8 rechargeable batteries with improved capacities and much smaller over-potentials. MgCl 2 was then further proven to be a powerful reagent to improve the performance of well-established strong Lewis acid derived magnesium electrolytes including the "all-phenyl" complex (APC) and alkoxide-based magnesium electrolytes. The results suggest that MgCl 2 salt is a very important species to benefit all chloride containing electrolytes for rechargeable magnesium-ion batteries.Currently, the lack of efficient energy storage devices is still the major limitation for the practical harvest of clean energies such as solar, wind or tide. Rechargeable batteries have been proposed as the promising solution for efficient energy storage and transmission. Although there is a great success of secondary lithium-ion batteries (LIBs) in portable electronic devices, the cost and safety barriers make traditional LIBs unable to meet the requirements for safe and economical power applications. As an alternative, magnesium-ion batteries are potential candidates for larger and safer energy storage due to the advantages in safety, cost and capacity. 1-3 For instance, in contrast to lithium, magnesium metal is non-toxic, more air resistant and free from dangerous dendrite formation. The greater natural abundance makes magnesium more than 20 times cheaper than lithium in cost. In addition, the divalent characteristic of magnesium ion (Mg/Mg 2+ ) enables magnesium to have nearly double the volumetric capacity versus lithium (3832 mA cm −3 vs 2062 mA cm −3 ). Despite these advantages, the lack of electrolytes which can plate/strip magnesium with wide electrochemical windows has retarded the progress of magnesium-ion batteries for quite a long time. 4 The discovery of efficient magnesium deposition can date back to early the 20 th century for Grignard reagents in ethereal solutions, but the relatively low oxidative stabilities (typically less than 2 V vs Mg/Mg 2+ ) prevented the use of Grignard reagents as effective electrolytes for high energy density secondary batteries. 5,6 The pioneering work by Gregory et al. in 1990 suggested that introducing strong Lewis acids into Grignard reagents can improve the oxidative stability, 7 and this strategy was later extended by Aurbach et al. in 2000 with the development of the famous dichloro-complex electrolyte (nBu 2 Mg + 2EtAlCl 2 ). 8 To date, strong Lewis acid neutralization has been proven one of the most successful methods to design magnesium electrolytes with more than 3 V (vs Mg/Mg 2+ ) stabilities, and it is believed that the addition of strong Lewis acids (aluminum or organoboron) helps to generate highly stable aluminate or organo-borate anions in solution, which in turn improves the oxidative st...

The synthesis of a terpyridine-appended, zinc-complexed cruciform, 3-Zn2+, and the anion-reactive modulation of its emissive properties in acetone-water mixtures are reported.