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In January 2013, airlines had to ground their fleets of Boeing Dreamliners due to fires linked to the "thermal runaway" of lithium-ion batteries. Likewise, lithium-ion-powered cars, such as the Tesla Model S, have caught fire "20 or so [times] in the past few years," sparking damaging viral videos (but still paling in comparison to the number of fires related to standard engines).1 Even more recently, a US teen's iPhone ignited in her back pocket because of its li-ion battery, an event the Daily Mail dutifully covered.
Possibly stopping more news flashes like these, this week in PNAS researchers described a design that addresses the flammability flaw.2 Rather than using the fire-prone alkyl carbonate electrolytes that most lithium-ion batteries employ, the team invented a nonflammable electrolyte with a class of compounds named the perfluoropolyethers, or PFPEs.
PFPEs have been applied as a lubricant for industrial machinery, but were being looked into as a way to prevent marine life from sticking to the bottom of ships. During this process, UNC-Chapel Hill researcher Joseph DeSimone noticed that the compound resembled in chemical structure an electrolyte already being investigated for lithium-ion devices.3
When he and his team demonstrated that PFPEs could also dissolve lithium salts, they proceeded to build a novel lithium-ion prototype, and with promising results. Tests have shown the battery to have a transference number — a measure of performance — of more than double that of conventional electrolytes.4 The prototype is stable above 200°C (~392°F) as well, making it a safer and more reliable design for larger-scale projects.
Moreover, it's not just the electrolyte-side of the battery, the part that carries the charge, that's lately been improved. Last month, University of Limerick researchers announced that they've built a better anode too, a part that the drives the charge.5
To do this, instead of working with the graphite most lithium-ion batteries use today, the team incorporated an element with a higher capacity, germanium. As this element tends to expand and shrink greatly during cycles, becoming increasingly brittle, the team intervened at the nano level to offset this characteristic. Specifically, they made an anode out of germanium standing nanowires, which restructured over time to form a "stable porous material" capable of withstanding more than 1,000 charging cycles.6
Taken together, these papers illuminate the potential of lithium-ion batteries and indicate that they can be durable, nonflammable, and energy-efficient. These advances could not only expand the horizon for electric cars, but also could lay the groundwork for lithium-ion power grids able to hold large stores of solar and wind energy without flaring up or falling apart.
Image credit: Photo of lithium-ion batteries from the Flickr stream of Argonne National Laboratory, a research hub in the US.
1. Bello, D. "Should Battery Fires Drive Electric Cars Off the Road?" Scientific American. November 12, 2013.
2. Wong, D. H. C., Thelen, J. L., Fu, Y., Devaux, D., Pandya, A. A., Battaglia, V. S., Balsara, N. P., and DeSimone, J. M. (2014). Nonflammable perfluoropolyether-based electrolytes for lithium batteries. PNAS DOI: 10.1073/pnas.1314615111
3. "Team Builds Nonflammable Lithium-Ion Battery." Phys.org. February 10, 2014.
4. Wong, et al., Ibid.
5. Kennedy, T., Mullane, E., Geaney, H., Osiak, M., O'Dwyer, C., Ryan, K. M. (2014). High-performance germanium nanowire-based lithium-Ion battery anodes extending over 1000 cycles through in situ formation of a continuous porous network. Nano Letters, 14, 716-723 PMID: 24417719
6. "Researchers Make Breakthrough in Battery Technology." R&D Magazine. February 10, 2014.
Thanks for reading!
For balance, you could have included some others that can easily be found by putting 'perfluoropolyether environment' into a search engine. This looks like yet another horse that has bolted.