NEWS
ENERGY STORAGE
Safer, long lasting batteries
MARIA BURKE
Lithium-ion batteries power everything from mobile devices to airliners and electric cars. But when overcharged, there is a risk of spontaneous combustion. Japanese scientists believe they have created a safer battery by introducing a flame-extinguishing chemical that doesn’t reduce performance. The problem with current Li-ion batteries
is that conventional carbonate electrolytes are highly flammable and volatile. Spontaneous combustion is not much of an issue with mobile devices, which are small and replaced frequently. But when the batteries are scaled up for use in electric cars or planes, their flammability problems are magnified and the consequences can be catastrophic. Researchers have tried introducing flame-
retardant solvents into electrolytes, but with mixed results. Often battery performance has been compromised because these solvents aren’t as good at making the carbon-rich anodes unreactive (passivation). To get around the problem, researchers at the
University of Tokyo led by Atsuo Yamada designed a concentrated electrolyte consisting of a salt and the flame-retardant solvent trimethyl phosphate, with no additives. A robust inorganic passivation film is reported to form spontaneously on the anode, allowing stable charge–discharge cycling of both hard-carbon and graphite anodes for more than 1000 cycles – over one year – with negligible degradation (Nature Energy, doi:10.1038/s41560-017-0033-8). This performance is as good or better than conventional carbonate electrolytes, they say. The technology could allow development of
bigger and more powerful lithium and sodium batteries, the researchers report. ‘This is a really important breakthrough. This
paper offers a new way to use highly concentrated (saturated) salt solutions with a minimal amount of solvent as non-flammable electrolyte,’ comments Yury Gogotsi, director of the A. J. Drexel Nanomaterials Institute In Philadelphia, US. However, he notes: ‘The paper primarily deals with sodium-ion batteries… considered as a low-cost alternative to ubiquitous lithium-ion batteries. They store less energy than lithium-ion batteries, but they are considered for storage of large amounts of renewable electrical energy from solar and wind warms. Making them safe is very important. At the end of the paper, the authors state that a similar approach is applicable to lithium-ion batteries and provide some data to support this statement in Supporting Information online.’
MARIA BURKE
Certain carbon nanotubes in manufacturing could pose the same cancer risk as asbestos, warn UK toxicologists. Their research gives new insights into mesothelioma, a rare cancer caused mainly by breathing in asbestos dust. Knowing more about its early stages could lead to earlier diagnosis and more effective therapies. Some carbon nanotubes are similar in size and shape to asbestos fibres. Used in making strong but lightweight materials – including special paints, sports equipment, boat hulls, aircraft, sports cars and computer motherboards – there is no evidence of risk from finished products. However, researchers have been
investigating the dangers involved in the manufacturing process. The team from the Medical Research Council Toxicology Unit in Leicester, UK, studied two groups of mice. In one group, they placed carbon nanotubes directly into the pleural space separating the lungs and chest wall, where mesothelioma usually develops; in the other group, they placed asbestos fibres. Previous studies have looked at the effect of introducing the fibres directly into the abdominal cavity of mice, but this approach more closely mimics occupational exposure. They found that asbestos fibres
and long nanotubes caused long- term inflammation in the pleural
space (Current Biol., doi:
http://dx.doi. org/10.1016/
j.cub.2017.09.007). Over time, this inflammation turns off the specific genes that suppress tumour formation, as happens in people with mesothelioma. However, the team stress that only certain carbon nanotubes are a concern.
‘Long, thin nanotubes have a very similar structure to asbestos,’ explains Anne Willis, director of the MRC Toxicology Unit. ‘The immune system does a good job of recognising shorter, thicker, or tangled up nanotubes. Special cells break down these types of fibre and clear them out of the body, so not all nanofibres pose a hazard.’ This is the first time the mesothelioma-causing effects of long and thin carbon nanotubes have been monitored in mice over many months, says senior author, Marion MacFarlane from the MRC. Researchers still don’t understand the molecular mechanisms underlying the long latency period of mesothelioma and what’s driving tumour development. ‘Because [mesothelioma] is diagnosed in humans when it’s quite advanced, we don’t know much about how or why it forms. This research could help us define key indicators for early detection as well as provide information for developing targeted therapies for this devastating disease.’ The researchers now plan to
investigate the role of tumour- suppressant proteins in carbon nanofibre-induced cancers.
NANOTECHNOLOGY
Nanofibre manufacturing risk
6
10 | 2017
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