mass of both reactants and a favorable 3.0 V potential. [3][4][5][6] The theoretical specifi c energy of 3505 Wh kg -1 , and energy density of 3435 Wh L -1 (based on Li 2 O 2 ), is very attractive compared to contemporary Li-ion couples that are calculated to have theoretical values near 400 Wh kg -1 and 1400 Wh L -1 . Practical values for Li-air batteries are estimated near 1000 Wh kg -1 , [ 7 ] which compare favorably to current Li-ion commercial cells (210 Wh kg -1 ), but realizing this specifi c energy over continuous operation requires surmounting many challenges in the underlying chemistry.The most prominent of these is creating an electrolyte for the non-aqueous cell which is inert to nucleophilic attack on discharge and charge of the battery, is stable to metallic lithium and solvates Li salts. Although the search for more stable systems has resulted in many investigations of different solvent/ salt combinations, it is generally agreed that there is presently no electrolyte that fi ts these requirements. Dimethylacetamide (DMA) [ 8 ] and dimethylformamide (DMF) [ 9 ] have recently been shown to be quasi-stable in combination with the LiTFSI salt. Nonetheless, both solvents react to form Li-X salts on cycling (X = formate, acetate and carbonate). [ 10 ] These decomposition products, particularly Li 2 CO 3, precipitate on the cathode where they increase impedance and create high cell polarization on charge owing to their high oxidation potentials. [11][12][13] Similar problems are created by the carbon support typically used for the gas diffusion membrane cathode which has been shown to react with the peroxide discharge product and produce Li 2 CO 3 interfacial impedance layers. [ 10 ] Two promising solutions to this dilemma have been presented by Peng et al., [ 14 ] who employed dimethyl sulfoxide (DMSO) as a solvent in combination with a nanoporous gold foil as a gas diffusion membrane, or Thotiyl et al., [ 15 ] utilizing TiC as a stable cathode material. Decomposition of DMSO leads to soluble products such as dimethyl sulfone and lithium sulfate, [16][17][18] which do not passivate the cathode surface to the same extent as do the carbonates. The high reactivity of DMSO with the lithium metal anode, and the eventual precipitation of the decomposition products renders this a fi rst-step solution. The higher rate capability of the noncarbonaceous cathode materials is also highly benefi cial because it favors formation of quasi-amorphous Li 2 O 2 thin-fi lms, which exhibit lower charging potentials. [ 19,20 ] TiC exhibits limited cycling behavior at fast rates even with tetraglyme (TEGDME).A new lithium-ether-derived chelate ionic liquid is synthesized to serve as an electrolyte for the Li-O 2 battery that is stable to metallic lithium, and whose ethereal framework is much more inherently stable to superoxide-initiated hydrogen abstraction than the simple glyme, dimethoxyethane (DME). Reactions of chemically generated superoxide with this electrolyte show that virtually no decomposition products such as lith...

Although Na-O2 batteries have a low overpotential and good capacity retention, degradation reactions of glyme-based electrolytes are the primary reason for inefficiency in cell performance. The discharge capacity is accounted for through analysis of the side-products. Although sodium superoxide is the primary product (90 % theoretical), quantitative and qualitative evaluation of the side-products (using (1) H NMR, iodometric titration, and on-line mass spectrometry) shows the presence of sodium acetate (∼3.5 %), and three-fold less sodium formate, methoxy (oxo)acetic anhydride, and sodium carbonate. Our reaction mechanism proposes two paths for their formation. Because the side-products are not fully removed during oxidation, they accumulate on the cathode upon cycling. Resting the cell at open circuit potential during discharge results in consumption of the superoxide through the reaction with diglyme, which greatly increases the fraction of side products, as also confirmed by ex situ reaction studies. These findings have implications in the search for more stable electrolytes.

The step-change in gravimetric energy density needed for electrochemical energy storage devices to power unmanned autonomous vehicles, electric vehicles, and enable low-cost clean grid storage is unlikely to be provided by conventional lithium ion batteries. Lithium-sulfur batteries comprising lightweight elements provide a promising alternative, but the associated polysulfide shuttle in typical ether-based electrolytes generates loss in capacity and low coulombic efficiency. The first new electrolyte based on a unique combination of a relatively hydrophobic sulfonamide solvent and a low ion-pairing salt, which inhibits the polysulfide shuttle, is presented. This system behaves as a sparingly solvating electrolyte at slightly elevated temperatures, where it sustains reversible capacities as high as 1200-1500 mAh g over a wide range of current density (2C-C/5, respectively) when paired with a lithium metal anode, with a coulombic efficiency of >99.7 % in the absence of LiNO additive.

A hypervalent iodine reagent-based α-carbonyl dihalogenation reaction is reported. Treating diazoacetate derivatives with either iodobenzene dichloride or iodotoluene difluoride results in gem-dichlorination or gem-difluorination products, respectively. The reaction is catalyzed by either Lewis acid or Lewis base activation of the aryl-λ(3)-iodane (ArIX2) species and proceeds rapidly and chemoselectively to the desired gem-difunctionalized products in good to excellent yield.

Af acile and highly chemoselective synthesis of doubly activated cyclopropanes is reported where mixtures of alkenes and b-dicarbonyl-derived iodonium ylides are irradiated with light from blue LEDs.This metal-free synthesis gives cyclopropanes in yields up to 96 %, is operative with cyclic and acyclic ylides,a nd proceeds with av ariety of electronicallydiverse alkenes.C omputational analysis explains the high selectivity observed, which derives from exclusive HOMO to LUMO excitation, instead of free carbene generation. The procedure is operationally simple,u ses no photocatalyst, and provides access in one step to important building blocks for complex molecule synthesis. Scheme 1. Light-mediated reactions of iodonium ylides.