Lithium-ion batteries currently reign supreme in their ability to hold a large amount of energy per weight, though they have rather complex charging requirements. Certainly lithium-ion batteries are not perfect, but they are good enough that almost every portable device today contains them. But nanowires might just replace lithium-ion batteries' popularity.
Nanowires are small wires, mere nanometers across, that tap into the properties of quantum mechanics due to their size. If you wish to learn more about nanowires, click here.
Utilizing gold nanowires, a battery was created by researchers at UC Irvine that was able to reach 200,000 discharge cycles with a 94-96% charge storage efficiency. This is unprecedented with lithium-ion batteries as they typically only last about 500+ charge cycles.
How do they work?
Since nanowires are so small, more surface area can be achieved in a smaller volume. This, in turn, allows for more charge to be stored.
Nanowires do, however, have an issue with cycle stability, or the breakdown of the nanowires as they are repeatedly charged. Transition metal oxides are used to help combat this issue, and the researchers at UC Irvine ended up using manganese oxide coupled with a poly (methyl methacrylate) gel electrolyte to achieve the large number of discharge cycles. This chemical combination allows for more stable nanowires as they resisted breaking down from repeated charging and discharging. While the gold nanowires proved to be the best in this case, they also tested lithium nanowires, which gave a comparatively lesser amount of stability.
A block diagram of the gold nanowire battery described. Image courtesy of UC Irvine (PDF).
It should be noted that these tests were done without positive and negative “terminals” (an anode and cathode), as this is by no means anywhere near a finished product phase. The battery created hardly resembles a battery, as it only composed of two cathodes, which is more beneficial in testing the charge cycles as they were linked together. While one cathode charged, the other discharged, and they went back and forth in this discharge cycle.
If you wish to read more about the specific work the researchers did, here is a link to their publication (PDF).
Magnified image of several nanowires and transition metal oxides. Image courtesy of UC Irvine (PDF).
How can they be useful?
Today, lithium-ion batteries are ubiquitous in all forms of mobile technologies, but they have a rather poor lifespan. Cell phone batteries last only a year before starting to drop off the charge capacity. Consumers end up having to get external batteries in the form of a case or large brick while waiting for their contract to expire to get a fresh new phone (assuming the battery is inaccessible). Laptops are notorious for losing battery life as they age, as well, and the battery replacements aren’t cheap.
Nanowire batteries can fix all of this since they have a tremendously long life. It is quite possible that nanowire batteries could provide mobile electronics a boost in their lifespan, as well, since these kinds of batteries wouldn’t need to be replaced for possibly decades. This is, of course, tentative— but the concept isn’t very far fetched. While supercapacitors are fantastic in their charge speed, they certainly won't be replacing traditional batteries anytime soon due to their low amount of stored energy.
Nanowire batteries are more likely to be the next battery technology that sweeps the market and finds its way into our pockets and offices. As the UC Irvine researchers outlined, gold nanowire batteries would be rather expensive, but it may be possible to replace the gold with nickel and still have the large number of charge cycles. Tests have not been conducted on nickel nanowires yet.