Enabled by the reversible conversion between Li2O2 and O2, Li-O2 batteries promise theoretical gravimetric capacities significantly greater than Li-ion batteries. The poor cycling performance, however, has greatly hindered the development of this technology. At the heart of the problem is the reactivity exhibited by the carbon cathode support under cell operation conditions. One strategy is to conceal the carbon surface from reactive intermediates. Herein, we show that long cyclability can be achieved on three dimensionally ordered mesoporous (3DOm) carbon by growing a thin layer of FeO(x) using atomic layer deposition (ALD). 3DOm carbon distinguishes itself from other carbon materials with well-defined pore structures, providing a unique material to gain insight into processes key to the operations of Li-O2 batteries. When decorated with Pd nanoparticle catalysts, the new cathode exhibits a capacity greater than 6000 mAh g(carbon) (-1) and cyclability of more than 68 cycles.

The Li-O2 battery promises high capacity to meet the need for electrochemical energy storage applications. Successful development of the technology hinges on the availability of stable cathodes. The reactivity exhibited by a carbon support compromises the cyclability of Li-O2 operation. A noncarbon cathode support has therefore become a necessity. Using a TiSi2 nanonet as a high surface area, conductive support, we obtained a new noncarbon cathode material that corrects the deficiency. To enable oxygen reduction and evolution, Ru nanoparticles were deposited by atomic layer deposition onto TiSi2 nanonets. A surprising site-selective growth whereupon Ru nanoparticles only deposit onto the b planes of TiSi2 was observed. DFT calculations show that the selectivity is a result of different interface energetics. The resulting heteronanostructure proves to be a highly effective cathode material. It enables Li-O2 test cells that can be recharged more than 100 cycles with average round-trip efficiencies >70%.

As a promising high-capacity energy storage technology, Li-O2 batteries face two critical challenges, poor cycle lifetime and low round-trip efficiencies, both of which are connected to the high overpotentials. The problem is particularly acute during recharge, where the reactions typically follow two-electron mechanisms that are inherently slow. Here we present a strategy that can significantly reduce recharge overpotentials. Our approach seeks to promote Li2O2 decomposition by one-electron processes, and the key is to stabilize the important intermediate of superoxide species. With the introduction of a highly polarizing electrolyte, we observe that recharge processes are successfully switched from a two-electron pathway to a single-electron one. While a similar one-electron route has been reported for the discharge processes, it has rarely been described for recharge except for the initial stage due to the poor mobilities of surface bound superoxide ions (O2(-)), a necessary intermediate for the mechanism. Key to our observation is the solvation of O2(-) by an ionic liquid electrolyte (PYR14TFSI). Recharge overpotentials as low as 0.19 V at 100 mA/g(carbon) are measured.

Enabled by the reversible conversion between Li 2 O 2 and O 2 ,L i-O 2 batteries promise theoretical gravimetric capacities significantly greater than Li-ion batteries.T he poor cycling performance,however,has greatly hindered the development of this technology.A tt he heart of the problem is the reactivity exhibited by the carbon cathode support under cell operation conditions.O ne strategy is to conceal the carbon surface from reactive intermediates.Herein, we show that long cyclability can be achieved on three dimensionally ordered mesoporous (3DOm) carbon by growing athin layer of FeO x using atomic layer deposition (ALD). 3DOm carbon distinguishes itself from other carbon materials with well-defined pore structures,providing aunique material to gain insight into processes key to the operations of Li-O 2 batteries.W hen decorated with Pd nanoparticle catalysts,t he new cathode exhibits ac apacity greater than 6000 mAh g carbon À1 and cyclability of more than 68 cycles.

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