News Energy storage Air batteries move ahead Anthony King


Future electric cars may run on lithium and air, a battery technology that could hold four times more energy than today’s most advanced batteries. Lithium-air batteries have a lithium metal anode, similar to today’s lithium ion batteries powering our phones and laptops, but they use oxygen from air as the active material at the cathode. This means the cathode requires porous carbon, a catalyst and oxygen, all lightweight. And there is no need for heavy Li intercalation compounds in Li-ion batteries, thereby improving the battery’s efficiency.


Lithium air batteries face a number of hurdles,


10.1021/nl4020952, resulting in poorly crystalline structures of lithium peroxide (Li2


however. Energy loss during charging and discharging occurs when the lithium ion reacts with oxygen at a cathode composed of carbon nanotubes (CNTs). Usually, crystalline byproducts insulate and cause energy loss. Scientists in Japan now report that energy loss can be reduced by adding nanoparticles made of ruthenium oxide (RuO2


researcher Hye Ryung Byon at RIKEN, Japan. ‘This Environment


O2 Anthony King


Nitrogen oxide (NOx) in diesel fumes has been blamed for disorienting honeybees in their search for flowers in a new lab study. But some bee scientists say the newspaper headlines were overblown and argue NOx would have little impact as wild bees may switch to odours not affected by diesel and can use other cues when seeking flowers.


In the study by University of Southampton researchers, NOx was reacted with a mix of eight floral chemicals taken from oilseed rape flowers and blended in the lab. The scientists reported that two of the volatile chemicals were rendered


with the conducting carbon cathode and a mostly amorphous structure, which has been simulated to be more conductive than crystalline Li2


‘Poorly-crystalline Li2O2


) to the cathode (Nano Letters, doi: O2


). has large contact area ,’ notes


results in promotion of Li2O2 decomposition during charging [Li2


nanoparticles and increased electrical efficiency of the battery,’ she explains. Efficiency here refers to the ratio of energy output and energy input to charge. The efficiency increased from 58% in


and decrease of charging over-potential. This shows on the reduced charging potentials we observe in our cathodes with RuO2


O2 --> 2Li+ + O2 Li2O2


CNT-only cathodes to 73% in CNT cathodes with RuO2


form and decompose Li2O2 rechargeable Li-O2


this depth of discharge the true energy density per total mass of the electrode is not much higher than in Li-ion batteries.’ The results are valid, ‘but it does not offer


comments Stefan Freunberger, battery chemist at Graz University of Technology, Austria. ‘A certain effect at not too deep discharge is frequently seen like here. The problem is that the very advantage of the Li-O2


O2 chemistry is not exploited since at nanoparticles. ‘Decomposition of


is very important since you can’t make a battery if you can’t efficiently in consecutive cycles,’


adds her colleague Ada Yilmaz. Efforts to influence crystallinity and defect density of the Li2


have been tried before,


energy density: deep discharge.


And it needs to do this at much faster rates than presented here, still lower over-potentials [energy efficiency], and for many more cycles.’ What is needed, he says, are breakthroughs in our scientific understanding of the reasons of capacity/ rate limitations.


a real solution for the problem addressed,’ says Freunberger. ‘To give said advantage over Li-ion it really needs to go towards the limits of theoretical


their high energy capacity, says Yilmaz: ‘We are expecting a mature Li-O2


Nevertheless, the strength of LiO2 battery to provide at


least 600 Wh/kg specific energy density, which is four times better than the Li-ion batteries we have today.’ says Yilmaz.


Diesel disorienting pollinators?


chemically undetectable in diesel polluted air within one minute; one of these chemicals (α -farnesene) made up 72.5% of the original odour blend (Scientific Reports, doi: 10.1038/ srep02779). The abundances of three other chemicals were reduced significantly. ‘We know that NOx is quite reactive and many of these volatile compounds are also naturally reactive, which can be a good thing as to work as signals, and animals and plants need them to disappear over time,’ says the lead author Guy Poppy. ‘What was remarkable here was the speed at which they disappeared, must faster than in ambient air.’ Honeybees were trained to associate this blend of floral chemicals


8 Chemistry&Industry • November 2013


with a sugary reward; when again exposed to the blend they stuck their tongue out in anticipation. While removing α-farnesene from the blend did not greatly reduce bee recognition, removing α-terpinene, which comprised just 0.8% of the blend, did significantly reduce bee response. When both chemicals were removed recognition dropped further. ‘When we exposed the bees to a mixture with only six of the remaining constituents the response dropped by [over] 30%,’ explains study author Tracey Newman. However, the bees had been


trained on the blend of eight chemicals and it is not known if bees could adjust to a reduced blend in the natural environment. They could refocus on


different chemical cues when exposed to a blend with components knocked out.


‘The fact that the diesel affects


floral cues is quite interesting and it could make it a bit harder for bees foraging on the edges of motorways and the like. It might slow them down a bit,’ says bumblebee scientist Dave Goulson at the University of Sussex, UK, ‘but not many habitats where bees forage have pollutant levels that high.’ Francis Ratnieks, also at the University of Sussex, adds: ‘This is a lab study. Bees have many backup mechanisms, and also recognise flowers by colour and location. I’d be surprised if the effect was harming bees in the field.’


batteries is + 2e-]


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