Power/Performance Bits: April 7

Hybrid supercapacitors

Researchers at UCLA combined the best qualities of batteries and supercapacitors in a new 3-D hybrid supercapacitor.

Based on laser-scribed graphene and manganese dioxide, the new component stores large amounts of energy, recharges quickly and can last for more than 10,000 recharge cycles. The team also created a microsupercapacitor small enough to fit in wearable or implantable devices. Just one-fifth the thickness of a sheet of paper, it is capable of holding more than twice as much charge as a typical thin-film lithium battery.

As a bonus, they can be fabricated without the need for extreme temperatures or expensive “dry rooms” currently required for supercapacitors.

The new hybrid supercapacitor developed at UCLA stores large amounts of energy, recharges quickly and can last for more than 10,000 recharge cycles. (Source: UCLA California NanoSystems Institute)

“Let’s say you wanted to put a small amount of electrical current into an adhesive bandage for drug release or healing assistance technology,” said Richard Kaner, distinguished professor at UCLA. “The microsupercapacitor is so thin you could put it inside the bandage to supply the current. You could also recharge it quickly and use it for a very long time.”

According to Kaner, “the LSG–manganese-dioxide capacitors can store as much electrical charge as a lead acid battery, yet can be recharged in seconds, and they store about six times the capacity of state-of-the-art commercially available supercapacitors.”

3-D scanners for everyone

A Caltech team’s development could bring cheap, compact 3-D imaging to consumer applications. The device, a nanophotonic coherent imager (NCI), used a silicon chip less than a millimeter square to provide the highest depth-measurement accuracy of any such nanophotonic 3-D imaging device.

The new chip utilizes an established detection and ranging technology called LIDAR, in which a target object is illuminated with scanning laser beams. The light that reflects off of the object is then analyzed based on the wavelength of the laser light used, and the LIDAR can gather information about the object’s size and its distance from the laser to create an image of its surroundings. “By having an array of tiny LIDARs on our coherent imager, we can simultaneously image different parts of an object or a scene without the need for any mechanical movements within the imager,” said Ali Hajimiri, professor of electrical engineering at Caltech.

The first proof of concept of the NCI has only 16 coherent pixels over an active area of 300 microns by 300 microns. However, the researchers also developed a method for imaging larger objects by first imaging a four-pixel-by-four-pixel section, then moving the object in four-pixel increments to image the next section. With this method, the team used the device to scan and create a 3-D image of the “hills and valleys” on the front face of a U.S. penny—with micron-level resolution—from half a meter away.

3D images produced by the new NCI chip. The images, taken from roughly half a meter (1.5 feet) away, shows the height of a US penny at various points (left) and an angled side view of the penny (right). (Source: Ali Hajimiri/Caltech)

In the future, according to Hajimiri, the current array of 16 pixels could also be easily scaled up to hundreds of thousands. By creating such vast arrays of these tiny LIDARs, the imager could be applied to a broad range of applications from very precise 3-D scanning and printing to helping driverless cars avoid collisions to improving motion sensitivity in superfine human machine interfaces.

Aluminum battery advancement

Aluminum has long been an attractive material for batteries, mainly because of its low cost, low flammability and high-charge storage capacity. But finding materials capable of producing sufficient voltage after repeated cycles of charging and discharging has been a key challenge of developing a commercially viable aluminum-ion battery.

An aluminum anode and graphite cathode along with an ionic liquid electrolyte was the winning combination for a Stanford University team, who created the first high-performance aluminum-ion battery that’s fast-charging, long-lasting and inexpensive.

The researchers reported “unprecedented charging times” of down to one minute with the aluminum prototype, which was also able to withstand more than 7,500 cycles without any loss of capacity.

Aluminum-ion technology also offers an environmentally friendly alternative to disposable alkaline batteries, said Hongjie Dai, professor of chemistry at Stanford. “Millions of consumers use 1.5-volt AA and AAA batteries. Our rechargeable aluminum battery generates about two volts of electricity. That’s higher than anyone has achieved with aluminum.”

But more improvements will be needed to match the voltage of lithium-ion batteries.

“Our battery produces about half the voltage of a typical lithium battery,” Dai said. “But improving the cathode material could eventually increase the voltage and energy density. Otherwise, our battery has everything else you’d dream that a battery should have: inexpensive electrodes, good safety, high-speed charging, flexibility and long cycle life. I see this as a new battery in its early days. It’s quite exciting.”