Tough Textile Batteries


With the launch of Google Glass and the Samsung Galaxy Gear wristwatch this year, wearable electronics have moved from abstract concepts to tangible products. To integrate these electronic devices seamlessly into clothing, watchbands, and backpacks, some engineers are developing flexible, powerful textile-based batteries. Now researchers in South Korea have built one of the most durable wearable batteries to date on polyester fabric (Nano Lett. 2013, DOI: 10.1021/nl403860k). The battery, which the researchers sewed into a shirt, can be folded 10,000 times without losing function.

Textile 1 1384358962084

Most attempts to make textile batteries have had limited success, says materials scientist Jang Wook Choi of the Korea Advanced Institute of Science and Technology (KAIST).

 

Fashionable Batteries            

            South Korean researchers fabricated lithium ion batteries on polyester cloth and then sewed them into a hoodie (left) and a watch wristband (right). The bottom cartoons show the shape of the batteries used in the shirt (left) and wristband (right).

The problem has been finding battery materials that can retain high function while being bent repeatedly. For example, batteries with metal foils as electrodes can bend only a few times before breaking. Electrodes made by dipping cloth in nanoparticle inks, such as solutions of carbon nanotubes, are more durable than the foils, but the electrical resistance of these cloth electrodes is relatively high, which limits the size of the batteries and the total amount of energy they can store.

Polyester Electrode            

            In a new textile battery, researchers fabricated electrodes by electroplating nickel onto polyester fabric (top, center). After adding the nickel layer, they completed the electrode by coating the fabric with a lithium electrode composite using a polyurethane binder (top, right). The nickel coated the individual fibers of polyester yarn, allowing the fabric to retain most of its mechanical properties (bottom, right). The electrode composite then coated each strand of yarn in the fabric. (below)

Textile 2 1384358970137To solve these challenges, Choi rethought the entire design of textile batteries, starting with the electrode. He turned to nickel, because it is a fantastic conductor. To make a flexible, but still highly conductive metal electrode, Choi came up with the idea of electroplating nickel onto polyester fabric. The process is simple, and the nickel-coated textile retains the mechanical properties of the fabric. The electrodes had a very low electrical resistance, about 0.35 ohms per square, comparable to that of a pure nickel metal foil.

The other critical component is the polymer used to bind the anode and cathode materials onto the electrodes in the battery. If this binder material fails, the battery will peel apart and stop functioning. Choi found that polyurethane had the right mechanical properties. To complete the battery, Choi’s group used conventional lithium-ion battery materials for the anodes and cathodes.

Choi’s group put the polyester-based batteries through their paces. Other groups have demonstrated bending and flexing of batteries, but the KAIST team thought the real test of mechanical durability would be to fold the device with firm creases. They powered an array of light-emitting diodes with the battery and folded it repeatedly. After 10,000 folding and unfolding cycles, the textile battery still worked. Batteries built with aluminum foil electrodes broke after three cycles and stopped working altogether after 100 cycles.

The KAIST group showed that their textile batteries can be sewn into a sweatshirt and a watchband. They also integrated the batteries with flexible solar cells so the batteries could recharge without needing to be removed from the clothing. “It’s quite comfortable to wear,” Choi says, adding that the battery is sealed so people could wash the fabric with the battery still attached.

“I’m really impressed,” says Yi Cui, a battery researcher at Stanford University. The KAIST group has successfully put their batteries through much harsher mechanical tests than others have been able to, he says.

The next step, Cui says, is to use battery materials that can store more energy to further improve the performance. So far, the KAIST team has used lithium iron phosphate for the cathode and lithium titanium oxide for the anode. Cui says that using a carbon anode material in the textile battery would increase the battery’s voltage, which determines how much power the device can deliver and how fast it can recharge. The voltage of the textile battery is about 2.5 V, and Choi says it should be about 3.8 V for practical applications.

Indeed, Choi’s group is experimenting with other materials, in collaboration with an unnamed South Korean battery maker that is interested in scaling up production of the wearable batteries.

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2013 American Chemical Society
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Mercedes Is Testing Google Glass Integration, and It Actually Works


imagesCAMR5BLR Einstein Judging a FishI put the car in park, unplug the phone, and put Google Glass on my face. Within seconds, I’ve got step-by-step directions to a coffee shop down the street beamed directly to my eyeballs. This is what Mercedes-Benz has planned for the future, and not only do they have a functioning prototype, they’re working with Google to make it a reality.

 

 

 

It’s called “Door-to-Door Navigation,” and it’s just the latest in a string of high-tech pushes the automaker has made in the past few years. It started with Mercedes doubling its resources and employees at its Silicon Valley research center, which allowed the automaker to work on a thoroughly revised infotainment platform and develop one of the first comprehensive integrations of Apple’s iPhone into its entry level and youth-focused CLA.

Now, it’s Google’s turn.

“We definitely see wearable devices as another trend in the industry that is important to us,” says Johann Jungwirth, Mercedes’ North American R&D President & CEO. “We have been working with Glass for roughly six months and meeting with the Google Glass team regularly.” And it’s helpful that Google HQ is just a 10-minute drive from the automaker’s Palo Alto research facility.

We’ve already established that cars are the killer app for Google Glass. And Mercedes agrees. The German automaker’s R&D center snagged two pairs of Google’s goggles as soon as they became available — recognizing the potential — and started hacking away.

The first application is a navigation program that allows you to enter an address through Google Glass, get in your car, plug in your phone, and then the destination is transferred to the in-dash navigation system. Once you’ve arrived near the restaurant/bar/nightclub/BBQ joint and unplug your phone, the system re-transfers the data back to Glass to complete the journey. And based on hands-on time, it works. But the way it works is … a little rough.

Google doesn’t offer Glass support for the iPhone. Yet. And the Mercedes “Digital DriveStyle App” doesn’t work with Android. Yet. (Jungwirth tells WIRED that iOS is the dominant platform for Mercedes owners). So in order for the destination information to be sent from the car to Glass, Mercedes connects to its own cloud server between the iPhone and the embedded infotainment system. Google Glass handles the communication between the two, and the trigger to communicate is the disconnection of the iPhone from the car. When that happens, it contacts the server, connects to Glass, and downloads the destination information.

Jungwirth is quick to point out that this elaborate dance of connections is just a proof of concept.

“This is, perhaps, not how we will accomplish it when we launch it as a product,” Jungwirth told WIRED. “As we are in talks with Google about making a direct connection to Glass work, but it is how our prototype works today.”

Jungwirth makes it clear that Mercedes has every intention of integrating some form of Google Glass functionality into its future products. And by the time Glass goes into production in the next year, Mercedes may have something to offer its customers. In the meantime, Jungwirth says that Android integration for Mercedes vehicles is coming in 2014.