Although dominating the consumer electronics markets as the power source of choice for popular portable devices, the common lithium battery is not yet suited for use in sustainable electrified road transport. The development of advanced, higher-energy lithium batteries is essential in the rapid establishment of the electric car market. Owing to its exceptionally high energy potentiality, the lithium-air battery is a very appealing candidate for fulfilling this role. However, the performance of such batteries has been limited to only a few charge-discharge cycles with low rate capability. Here, by choosing a suitable stable electrolyte and appropriate cell design, we demonstrate a lithium-air battery capable of operating over many cycles with capacity and rate values as high as 5,000 mAh g(carbon)(-1) and 3 A g(carbon)(-1), respectively. For this battery we estimate an energy density value that is much higher than those offered by the currently available lithium-ion battery technology.

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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.

MgTFSI 2 is the only ether-soluble "simple" magnesium salt. The poor electrochemical performance of Mg electrodes in its solutions hinders its practicality as a viable electrolyte for Mg batteries. MgTFSI 2 /DME solutions were demonstrated to dissolve large quantities of MgCl 2 and produce electrolyte solutions with superior performance, though the electrochemical performance, mainly in terms of reversibility, of MgTFSI 2 /MgCl 2 (DME) solutions cannot yet compete with that of organometallic based electrolyte solutions. We believe that the solutions' purity level governs the overall electrochemical performance, especially in solutions where a strong reductant (i.e Grignard reagent) is not present to act as an impurity scavenger. In this work, we alter the performance of the MgTFSI 2 /MgCl 2 (DME) solutions through chemical and electrochemical conditioning and demonstrate the effect on the solutions' electrochemical characteristics. We demonstrate relatively high reversible behavior of Mg deposition/dissolution with crystalline uniformity of the Mg deposits, complemented by a fully reversible intercalation/de-intercalation process of Mg ions into Mo 6 S 8 cathodes. We also investigated LiTFSI/MgCl 2 solutions which exhibited even higher reversibility than MgTFSI 2 /MgCl 2 (DME) solutions, which we attribute to the higher purity level available for the LiTFSI salt. Magnesium is a natural candidate anode material for "next generation" rechargeable batteries due to its high volumetric capacity (3833 mAh/cm 3 ), low reduction potential (−2.3 V) wide abundance, and low price.1 Rechargeable Mg battery research had been developing very slowly since the 1920's but had recently gained a big momentum. Magnesium battery systems will have great difficulties to outperform lithium systems In terms of energy and power density. However, they possess several properties that make them desirable, as they are expected to benefit from a cheaper price and lower hazard levels. One of the core issues developing rechargeable magnesium batteries is the formulation of electrolytic solutions that support reversible magnesium deposition. Other properties such as sufficient ionic conductivity, adequate magnesium ion concentration, and a wide electrochemical window are also mandatory. 15 years ago we synthesized electrolyte solutions that possessed most of the key features listed above. These electrolyte solutions were the product of a Lewis acid/base reaction in which R 2 Mg moieties such as Bu 2 Mg served as the base component, and RAlCl 2 species such as EtAlCl 2 served as the acid component.Hence, we could demonstrate a family of organometallic electrolyte solutions for rechargeable Mg batteries known as di-chloro complex solutions (DCC).2,3 Unfortunately, even the best DCC electrolyte solution does not possess the minimum requirement needed for next generation rechargeable magnesium batteries, e.g. wide electrochemical stability window (>2.2 V), chemical stability and safety. The use of aromatic ligands enabled to develop electrolyte solu...

gas. At the same time, the penetration of renewable energy sources has opened up the possibility of creating a CO 2 -neutral mobility system, where electric vehicles are powered by wind, hydro, and solar energy.Broad fi nancial efforts are being made at a governmental and industrial level to fund research into new areas of energy storage. The U.S. Department of Energy has allocated $20 million to energy storage research in 2012 and $15 million the following year, while the German government has committed itself to ¤200 million between 2011 and 2018; [ 1 ] similar schemes are also being promoted in Japan by the New Energy and Industrial Technology Development Organization (NEDO). The EU-backed "Horizon 2020" program aims at funding research into energy storage technologies, a fi eld where the European Union lags behind the U.S. and East Asia. [ 2 ] Lithium-ion technology has established itself as a type of reliable energy-storage chemistry over the past 20 years, fi rst being used in camcorders, then mobile phones, laptops, and more recently electric cars. However, as the size of the battery pack increases, so does the belief that the cost per kW h and its energy density are not suitable for practical vehicle applications. The Tesla Model S, which sports a 400 km driving range, does so with a whopping 85 kW h battery pack that alone has up to twice the price of a standard economy car. With a current cost higher than 400 $ kW h −1 , electric cars have so far only entered a niche, high-end market where users are willing to pay a premium. Resizing the battery pack, and so the total cost of an electric car, results in a limited driving range (typically 100-150 km) that automatically restricts the use for long-haul journeys and triggers the so-called "range anxiety" feeling. For these reasons, the need to develop energy-storage technologies that enable at least a 500 km driving range, while retaining the same battery pack volume at an affordable price, is of primary interest for governments and car manufacturers. A Brief History of Lithium/Air BatteriesOver the years, the scientifi c community has focused its interest on advanced lithium-ion and fuel cells with only incremental improvements being made. Lithium-ion technology in particular is predicted to reach an asymptotic limit in specifi c Lithium/air is a fascinating energy storage system. The effective exploitation of air as a battery electrode has been the long-time dream of the battery community. Air is, in principle, a no-cost material characterized by a very high specifi c capacity value. In the particular case of the lithium/air system, energy levels approaching that of gasoline have been postulated. It is then not surprising that, in the course of the last decade, great attention has been devoted to this battery by various top academic and industrial laboratories worldwide. This intense investigation, however, has soon highlighted a series of issues that prevent a rapid development of the Li/air electrochemical system. Although several breakthroughs have be...