Power/Performance Bits: Nov. 19

Quantum communications chip
Researchers at Nanyang Technological University, Australian National University, A∗STAR, University of Science and Technology of China, Singapore University of Technology and Design, Sun Yat-sen University, Beijing University of Posts and Telecommunications, and National University of Singapore built an integrated silicon photonic chip capable of performing quantum key distribution.

At about 3mm, the chip is much smaller than current quantum communications systems and uses standard industry materials, making it easier to manufacture. Aside from the laser source, all optical components are integrated on the chip. It is compatible with existing fiber optical communications infrastructure.

“In today’s world, cyber security is very important as so much of our data are stored and communicated digitally,” said Liu Ai Qun, a professor at NTU Singapore. “Almost all digital platforms and repositories require users to input their passwords and biometric data, and as long as this is the case, it could be eavesdropped on or deciphered. Quantum technology eliminates this as both the password and information are integrated within the message being sent, forming a ‘quantum key’.”

Roughly about 3mm in size, the tiny chip developed by NTU scientists uses quantum communication algorithms to better security than existing industry standards. It also opens doors for more secure communication technologies that can be deployed in compact devices such as smartphones, tablets and wearables. (Source: NTU Singapore)

Quantum communication works by using randomized strings of code to encrypt the information, which can only be opened by the intended recipient with the correct ‘key,’ according to Kwek Leong Chuan, a physicist and associate professor at NTU Singapore. “It is like sending a secured letter. Imagine that the person who wrote the letter locked the message in an envelope with its ‘key’ also inside it. The recipient needs the same ‘key’ to open it. Quantum technology ensures that the key distribution is secure, preventing any tampering to the ‘key.’”

The team is planning to develop a hybrid network of traditional optical communication systems and quantum communication systems, which they believe will improve the compatibility of quantum technologies that can be used in a wider range of applications such as internet connectivity.

Faster battery charging with heat
Engineers at Pennsylvania State University found a way to charge lithium-ion batteries for electric vehicles much more quickly, and with less degradation, using high temperatures.

“We demonstrated that we can charge an electrical vehicle in ten minutes for a 200 to 300 mile range,” said Chao-Yang Wang, Chair of mechanical engineering, professor of chemical engineering and professor of materials science and engineering, and director of the Electrochemical Engine Center at Penn State. “And we can do this maintaining 2,500 charging cycles, or the equivalent of half a million miles of travel.”

When lithium-ion batteries are rapidly charged at ambient temperatures under 50 F, lithium deposits form on the battery’s anode, reducing cell capacity and potentially causing dangerous battery failure.

A previous effort by the team resulted in a battery that could charge in 15 minutes at 50 F. While higher temperatures would lead to more efficient charging, prolonged exposure to heat also degrades the batteries.

“Taking this battery to the extreme of 60 degrees Celsius (140 degrees F) is forbidden in the battery arena,” said Wang. “It is too high and considered a danger to the materials and would shorten battery life drastically.”

Instead, the team found that by heating the batteries to 60 C (140 F) for just ten minutes, then rapidly cooling it to ambient temperature, neither the lithium spikes formed nor did heat-related degradation occur. The battery could also sustain the extremely fast charging process for 1,700 cycles.

“In addition to fast charging, this design allows us to limit the battery’s exposure time to the elevated charge temperature, thus generating a very long cycle life,” said Wang. “The key is to realize rapid heating; otherwise, the battery will stay at elevated temperatures for too long, causing severe degradation.”

The batteries are self-heating using a thin nickel foil with one end attached to the negative terminal and the other extending outside the cell to create a third terminal. A temperature sensor attached to a switch causes electrons to flow through the nickel foil to complete the circuit. This rapidly heats up the nickel foil through resistance heating and warms the inside of the battery. For cooling, the battery could take advantage of the car’s cooling system.

The researchers say the technology is completely scalable because all the cells are based on industrially available electrodes; and they have already demonstrated its use in large-scale cells, modules, and battery packs. The nickel foil increases the cost of each cell by 0.47%, but because the design eliminates the need for the external heaters used in current models, it actually lowers the cost of producing each pack.

“The 10-minute trend is for the future and is essential for adoption of electric vehicles because it solves the range anxiety problem,” said Wang. And the team plans to continue working on fast-charging, high-temp batteries. “We are working to charge an energy-dense electric vehicle battery in five minutes without damaging it. This will require highly stable electrolytes and active materials in addition to the self-heating structure we have invented.”

Faster charging with light
Researchers at Argonne National Laboratory took a different approach to speeding up electric vehicle battery charging: exposing the cathode to a beam of concentrated light. This light exposure decreased lithium-ion battery time by a factor of two or more.

Typically, charging an electric car’s battery from empty takes about eight hours. “We wanted to greatly shorten this charge reaction without damaging the electrodes from the resulting higher current flow,” said Christopher Johnson, Argonne Distinguished Fellow and group leader in the Chemical Sciences and Engineering division.

Instead of a typical opaque case, the new battery would use a transparent container that allows concentrated light to illuminate the battery electrodes during charging. The cathode material was lithium manganese oxide (LiMn2O4 or LMO).

In tests, the team used small coin cell lithium-ion batteries with transparent quartz windows which were exposed or not exposed to white light. “We hypothesized that, during charging, white light would interact favorably with the typical cathode material, and that proved to be the case in our cell tests,” Johnson said.

While absorbing the photons in the light during charging, the element manganese in the LMO changes its charge state from trivalent to tetravalent (Mn3+ to Mn4+). In response, lithium ions eject faster from the cathode than would occur without the photon-excitation process. This condition drives the battery reaction faster. The team found that the faster reaction resulted in faster charging without degrading battery performance or cycle life. “Our cell tests showed a factor of two decrease in charging time with the light turned on,” Johnson said.

The Vehicle Technologies Office of the DOE Office of Energy Efficiency and Renewable Energy has identified fast charge as a critical challenge in ensuring mass adoption of electric vehicles with a goal of 15-minute recharge time.

Johnson added, “This finding is the first of its kind whereby light and battery technologies are merged, and this intersection bodes well for the future of innovative charging concepts for batteries.”