Power/Performance Bits: March 2

Fast-charging EV battery
Electric vehicle adoption faces challenges from consumers’ range anxiety and the extended lengths of time needed to charge a car’s battery. Researchers at Pennsylvania State University are trying to address this by developing lithium iron phosphate EV batteries that have a range of 250 miles with the ability to charge in 10 minutes. It also is expected to have a lifetime 2 million miles.

“We developed a pretty clever battery for mass-market electric vehicles with cost parity with combustion engine vehicles,” said Chao-Yang Wang, chair of mechanical engineering, professor of chemical engineering, professor of materials science and engineering, and director of the Electrochemical Engine Center at Penn State. “There is no more range anxiety and this battery is affordable.”

Key to the battery’s quick charging is its self-heating ability. The battery uses a thin nickel foil with one end attached to the negative terminal and the other extending outside the cell to create a third terminal. Once electrons flow it rapidly heats up the nickel foil through resistance heating and warm the inside of the battery. When the battery’s internal temperature is 140 degrees F, the switch opens and the battery is ready for rapid charge or discharge.

Because of the fast charging, energy density was of less importance and lower cost materials could be used. The cathode is lithium iron phosphate, without expensive cobalt, while the anode is very large particle graphite. A low-voltage electrolyte was also used. The researchers also expect it to be safer, without concerns about uneven deposition of lithium on the anode, which can cause lithium spikes and battery failure.

“This battery has reduced weight, volume and cost,” said Wang. “I am very happy that we finally found a battery that will benefit the mainstream consumer mass market.”

DNA origami nanowires
Researchers from Bar-Ilan University, Ludwig-Maximilians-Universität München, Columbia University, and Brookhaven National Laboratory are using DNA origami, a technique that can fold DNA into arbitrary shapes, as a way to create superconducting nanostructures.

The DNA origami nanostructures are comprised of two major components, a circular single-strand DNA as the scaffold, and a mix of complementary short strands acting as staples that determine the shape of the structure.

“In our case, the structure is an approximately 220-nanometer-long and 15-nanometer-wide DNA origami wire,” said Lior Shani, of Bar-Ilan University. “We dropcast the DNA nanowires onto a substrate with a channel and coat them with superconducting niobium nitride. Then we suspend the nanowires over the channel to isolate them from the substrate during the electrical measurements.”

The team said the DNA origami technique can be used to fabricate superconducting components that can be incorporated into a wide range of architectures and that are not possible to construct with conventional fabrication techniques.

“Superconductors are known for running an electric current flow without dissipations,” said Shani. “But superconducting wires with nanometric dimensions give rise to quantum fluctuations that destroy the superconducting state, which results in the appearance of resistance at low temperatures.”

However, the group was able to use a high magnetic field to suppress these fluctuations and reduce about 90% of the resistance.

“This means that our work can be used in applications like interconnects for nanoelectronics and novel devices based on exploitation of the flexibility of DNA origami in fabrication of 3D superconducting architectures, such as 3D magnetometers,” continued Shani.

Tiling nanosheets
Nanosheets hold potential for making transparent and flexible electronics, optoelectronics, and power harvesting devices. However, current methods of tiling nanomaterials such as titanium dioxide can be time-consuming, expensive, and wasteful. Researchers at Nagoya University and the National Institute for Materials Science in Japan propose a simpler one-drop approach to tiling nanosheets in a single layer.

“Drop casting is one of the most versatile and cost-effective methods for depositing nanomaterials on a solid surface,” said Minoru Osada, a materials scientist at Nagoya University. “But it has serious drawbacks, one being the so-called coffee-ring effect: a pattern left by particles once the liquid they are in evaporates. We found, to our great surprise, that controlled convection by a pipette and a hotplate causes uniform deposition rather than the ring-like pattern, suggesting a new possibility for drop casting.”

The team’s process involves dropping a solution containing 2D nanosheets with a simple pipette onto a substrate heated on a hotplate to a temperature of about 100°C, followed by removal of the solution. This causes the nanosheets to come together in about 30 seconds to form a tile-like layer.

They found that the nanosheets were uniformly distributed over the substrate, with limited gaps. The researchers noted this is likely a result of surface tension driving how particles disperse, and the shape of the deposited droplet changing as the solution evaporates.

The process was used to deposit particle solutions of titanium dioxide, calcium niobate, ruthenium oxide, and graphene oxide. A variety of substrates were used, including silicon, silicon dioxide, quartz glass, and polyethylene terephthalate (PET) in different sizes and shapes. Surface tension and evaporation rate could be controlled by adding a small amount of ethanol to the solution.

The method was also used to deposit multiple layers of tiled nanosheets, creating functional nanocoatings with conducting, semiconducting, insulating, magnetic, or photochromic features. “We expect that our solution-based process using 2D nanosheets will have a great impact on environmentally benign manufacturing and oxide electronics,” said Osada.