Power/Performance Bits: Feb. 2

MXene antennas
Researchers at Drexel University and Villanova University developed spray-on antennas made of the 2D materials MXene that is flexible and light while maintaining good signal.

“This combination of communications performance with extreme thinness, flexibility and durability sets a new standard for antenna technology,” said Yury Gogotsi, professor of Materials Science and Engineering in Drexel’s College of Engineering. “While copper antennas have been the best in terms of performance for quite some time, their physical limitations have prevented connected and mobile technology from making the big leaps forward that many have predicted. Due to their unique set of characteristics MXene antennas could play an enabling role in the development of IoT technology.”

The team said the MXene antenna is capable of performing at frequencies used for 5G, showing comparable performance to copper antennas at 28 GHz. The three sets of antennas tested ranged between 7-14 times thinner and 15-30 times lighter than a similar copper antenna.

The team of Drexel researchers fabricated and tested a series of ultrathin, flexible MXene antennas, which can be spray applied to a variety of surfaces. (Credit: Drexel University)

Plus, the antennas can be spray applied, screen printed or inkjet-printed onto various substrates and remains flexible without sacrificing performance.

“Generally copper antenna arrays are manufactured by etching printed circuit boards, this is a difficult process to undertake on a flexible substrate,” said Meikang Han, a post-doctoral researcher at the A.J. Drexel Nanomaterials Institute. “This puts MXene at a distinct advantage because it disperses in water to produce an ink, which can be sprayed or printed onto building walls or flexible substrates to create antennas.”

In tests, the MXene antennas performed within 5% percent of copper antennas, with performance increasing with thickness of the antenna. The best performing MXene patch antenna, about one-seventh the thickness of standard copper antennas, was 99% as efficient as a copper antennas operating at 16.4 GHz frequency in an open environment. MXenes were also 98% as effective as their copper counterparts operating in the 5G frequency. The antennas were able to undergo as many as 5,000 bending cycles without losing performance.

“MXene’s scalability and environmental sustainability in manufacturing has been well established, for this material to now achieve performance goals on pace with the best materials on the market today is certainly a significant development,” Gogotsi said. “As we continue to test various coating patterns and techniques while additionally optimizing the composition of MXene materials, I expect their performance to continue to improve.”

Recycling Li-ion batteries
Engineers at University of California San Diego, Argonne National Laboratory, Oak Ridge National Laboratory, and University of California Riverside propose a more environmentally friendly method to recycle lithium-ion batteries.

The process is targeted at cathodes made from lithium iron phosphate, or LFP. LFP cathode batteries are less expensive because they don’t use cobalt or nickel. They are frequently used in power tools, electric buses, and energy grids, as well as in Tesla’s Model 3.

“Given these advantages, LFP batteries will have a competitive edge over other lithium-ion batteries in the market,” said Zheng Chen, a professor of nanoengineering at UC San Diego. However, “It’s not cost-effective to recycle them. It’s the same dilemma with plastics–the materials are cheap, but the methods to recover them are not.”

The researchers said the new method uses greener ingredients, consumes 80 to 90% less energy, and emits about 75% less greenhouse gases compared to alternative ways of recycling Li-ion batteries. It operates at low temperatures (60 to 80 C) and ambient pressure and uses the inexpensive, benign materials lithium salt, nitrogen, water, and citric acid.

“The whole regeneration process works at very safe conditions, so we don’t need any special safety precautions or special equipment. That’s why we can make this so low cost for recycling batteries,” said Panpan Xu, a postdoctoral researcher at UC San Diego.

First, the team cycled commercial LFP cells until they had lost half their energy storage capacity. They took the cells apart, collected the cathode powders, and soaked them in a solution containing lithium salt and citric acid. Then they washed the solution with water, dried the powders and heated them.

The researchers made new cathodes from the powders and tested them in both coin cells and pouch cells. Their electrochemical performance, chemical makeup and structure were all fully restored to their original states.

The process restores the cathode’s structure by replenishing lithium ions and making it easy for iron and lithium ions to switch back to their original spots.

However, the team noted that more study is needed on the logistics of collecting, transporting and handling large quantities of batteries. “Figuring out how to optimize these logistics is the next challenge,” Chen said. “And that will bring this recycling process closer to industry adoption.”

Mid infrared sensing
Researchers at the University of Texas at Austin and Omega Optics developed a chip for communications and sensing that is more resistant to the impacts of poor weather conditions.

The indium phosphide chip operates in the mid infrared spectrum, which allows signal to penetrate through clouds, rain, and other weather without shedding significant amounts of light. “Low light loss means signal can travel further, and through the earth’s atmosphere, with better integrity and less power consumption,” said Ray Chen, professor in the Cockrell School of Engineering’s Department of Electrical and Computer Engineering at UT Austin.

The device is capable of beam steering, allowing it to re-direct light in the direction of a specific target.

Typically, beam steering can only bounce light in narrow directions. The new device has much wider angles for steering light, increasing the range by about 30 degrees compared to other options, without moving parts or side lobes of light that trail off in various directions and decrease efficiency.

The team sees potential for the technology in sensing vehicle surroundings, and it would not need to spin like lidar arrays. The mid infrared range can also be used for environmental sensing, picking up things like gas leaks and smoke stack emissions. Another potential applications is free-space optical communication, and the researchers are planning on investigating this aspect further with field testing and optimization.