The list of things with lithium-ion batteries just keeps growing. Smartphones, tablets, laptops, game controllers, cordless power tools, grooming products, digital cameras, camcorders, e-cigarettes, cars and more all rely on lithium-ion batteries. It’s great to have this stuff but keeping everything charged gets to be a problem. Researchers at the University of Central Florida's NanoScience Technology Center have nanoengineered a possible solution.
Unlike a battery that stores energy through a chemical process, capacitors store energy using static electricity. Static electricity is what's in play when your clothes stick together when you take them out of the dryer.
Capacitors have some significant advantages over batteries as energy storage devices. For example, they charge and discharge much faster, they’re lighter in weight, they don’t wear out as fast and they don’t contain toxic and dangerous chemicals. Supercapacitors, sometimes called ultracapacitors, can store orders of magnitude more energy than regular capacitors.
If capacitors are so good, why don’t we have supercapacitors in all our electronic devices? They’re too large. You need a supercapacitor that is too big to be practical to store the same amount of energy as the lithium-ion battery in a smartphone or laptop.
This is where nanoengineering comes into the picture. The researchers at the University of Central Florida created supercapacitors made from nanowires composed of a one-dimensional core (made of highly single-crystalline tungsten trioxide) wrapped with two two-dimensional shells (made of tungsten disulfide) that are separated by a subnanometer gap. The research is reported in the American Chemical Society journal Nano.
These nanowire supercapicitors solve the size problem. Materials at the nanoscale have at least one dimension of less than roughly 100 nanometers where a nanometer is one millionth of a millimeter which is about 100,000 times smaller than the diameter of a human hair. You can put millions of nanowires in the same volume occupied by the lithium-ion battery in a cell phone.
Combining millions of nanowires produces a supercapacitor with properties that make them ideal replacements for lithium-ion batteries. For example, they charge and discharge extremely quickly. Recharge speed is so fast that electronic devices equipped with nanowire supercapacitors could be charged in seconds and the charge would last for more than a week of normal use according to Nitin Choudhary the postdoc associate who synthesized the nanowires. The rapid discharge rate would allow cars equipped with nanowire supercapacitors to accelerate more quickly than electric cars equipped with lithium-ion batteries.
Another advantage is that nanowire supercapacitors don’t wear out like lithium-ion batteries. An average lithium-ion battery lasts for 1,000 to 1,500 recharge cycles. Recharging your phone twice after it drops to a 50% charge counts as one recharge cycle. The nanowire supercapacitors, on the other hand, showed no decline in performance after they had undergone 30,000 recharge cycles.
If all of that isn’t enough, the nanowire supercapacitors are situated on a flexible substrate that could be molded into desired shapes or incorporated into wearables. Imagine a voice-activated phone plus digital assistant with a full array of sensors that lives in your shirt. Hustling down the street while trying not to sweat you ask, “Aliri, how late am I going to be for the big meeting and how’s my deodorant holding up?”
At this stage of development, the nanowire supercapacitors are a proof of concept that is not ready for commercial adoption. The University of Central Florida’s Office of Technology Transfer is working to patent the technology.
