Imagine you’re hiking in the mountains when a blizzard hits. Despite your warm coat, your body temperature begins to drop. But fear not. Temperature sensors in the coat feel you getting colder, activating heating elements embedded in the fabric. Perfectly toasty, you continue your hike.
Sounds like a smart idea, right? Why is it not a reality? In a word, batteries. Battery technology has not advanced as quickly as wearable technology, meaning wearables—smartwatches, fitness trackers, clothing-embedded medical sensors—must either be equipped with bulky batteries or plugged in to charge at frequent intervals.
Now, researchers in the UK have a new development that could lead to a solution: a flexible, battery-like device made of graphene that can be printed directly on almost anything.
“You can print the batteries on a flexible substrate like textiles,” says Mohammad Nazmul Karim, a fellow at the National Graphene Institute at the University of Manchester. “And it can be charged very rapidly.”
The devices, recently described in the journal 2D Materials, are technically not batteries but supercapacitors, which store energy on their surfaces by static charge. They can be charged extremely quickly compared to batteries—in seconds, rather than minutes or hours—and don’t lose their energy storage capabilities over time, even after millions and millions of charges.
The supercapacitors developed by Karim and his team are made from graphene, a two-dimensional lattice of carbon only one atom thick. The researchers used a basic screen printing technique to print a flexible supercapacitor of graphene-oxide ink onto cotton fabric. The fabric can be worn, stretched and even thrown in the wash without destroying the supercapacitor’s charging capabilities.
“If you have a piece of fabric and you apply graphene on that fabric, it doesn’t only make it conductive, it also makes it stronger,” Karim says.
Graphene can be stretched up to 20 percent larger than its original size without breaking. This is one of the reasons it’s considered so promising for wearables, which need to move with the body.
The team’s initial goal is to use the graphene supercapacitors for medical sensors: wearable heart monitors, temperature sensors and EEG sensors to monitor sleep and other brain activities. This could happen in as little as two or three years, Karim estimates. Other uses—clothes the charge your cell phone, wearable computers, even the temperature-stabilizing jacket I described—would be significantly further down the road.
Wearable technology—everything from smartwatches to fitness trackers to wearable cameras to clothing-embedded medical sensors—is big business. A recent analysis by CCS Insight suggests the industry will be worth some $34 billion by 2020. But charging has been a constant problem for wearables developers. Nobody wants to take their wristband off to charge in the middle of the day. So the search for better batteries and alternative charging solutions has been going on for years. Many companies have banked on wireless charging as the wave of the future for wearables—you could simply walk into your kitchen, and have your device charged by a wireless charger on the wall while you cook dinner, without even taking it off. But the technology is still very much under development, and consumers have been slow to warm to the relatively slow and expensive wireless chargers on the market so far.
Karim cautions that graphene is no silver bullet either.
“There’s lots of hype around graphene, and we need to be careful,” he says.
One major challenge is making large quantities of high quality graphene. It’s cheap and easy to make lower quality graphene, which is fine for some applications. But the best quality of graphene is still expensive and laborious to produce, a problem researchers are working on.
“Maintaining the high quality of graphene in a scalable quantity is a huge challenge,” Karim says.
Another drawback to graphene is that it doesn’t conduct electricity as well as metals. So while graphene-based supercapacitors are strong and flexible, as well as relatively environmentally friendly, silver or copper supercapacitors are more conductive. Depending on the use, one or the other might be preferable.
So watch this space. In a decade or two, we might be describing the new, graphene supercapacitor-powered winter jacket, perfect for your next trip to the Himalayas.