Power/Performance Bits: Nov. 3

Wirelessly charging multiple devices
Researchers from ITMO University developed a metamaterial that can be used to turn surfaces into wireless charging areas for multiple devices from different manufacturers with different power transfer standards.

“There are various wireless power transfer standards with different frequencies, so you can’t just use a charger by any manufacturer,” said Polina Kapitanova, a researcher at ITMO University’s Department of Physics and Engineering. “For example, Huawei uses one wireless power transfer frequency for mobile phones and another – for smart glasses, so you can’t charge these devices with the same charger.”

“What we propose is a brand-new metasurface that can be used as a transmitter in the wireless power transfer system that would allow users to charge several devices at once,” continued Kapitanova. “This surface can be used at one frequency or at several.”

Instead of conventional flat coil resonators, the metasurface uses a resonator formed as an array of sub-wavelength parallel strip conductors. The system can be spread over a wide area, such as an end table or nightstand.

“As it turned out, this structure has unique properties, including reverse frequency dispersion that can be efficiently applied in wireless power transfer,” said Kapitanova. “This structure has several modes (resonant frequencies) that have a uniform magnetic field. It allows us to transfer energy wirelessly. At the same time, the electric field is hidden at the edges of the structure, at the capacitors, and it’s safer for users that way.”

The researchers created a prototype of the metasurface and studied its properties with different frequencies as part of a smart table project and successfully lit LEDs with different frequencies. Next, the team plans to evaluate the level of decrease in the electric field in order to make the charger safer and faster.

Light, plant-based supercapacitor
Researchers at Texas A&M University and Lawrence Berkeley National Laboratory developed a supercapacitor based on manganese dioxide and the plant-based polymer lignin.

“Integrating biomaterials into energy storage devices has been tricky because it is difficult to control their resulting electrical properties, which then gravely affects the devices’ life cycle and performance. Also, the process of making biomaterials generally includes chemical treatments that are hazardous,” said Dr. Hong Liang, professor in the Department of Mechanical Engineering at TAMU. “We have designed an environmentally friendly energy storage device that has superior electrical performance and can be manufactured easily, safely and at much lower cost.”

To develop one of the electrodes in a supercapacitor, the team investigated manganese dioxide. “Manganese dioxide is cheaper, available in abundance and is safer compared to other transition metal oxides, like ruthenium or zinc oxide, that are popularly used for making electrodes,” said Liang. “But a major drawback of manganese dioxide is that it suffers from lower electrical conductivity.”

Lignin, the natural polymer that makes wood fibers stick together, has been shown to enhance the electrochemical properties of other metal oxide electrodes. The team treated purified lignin with the disinfectant potassium permanganate. High heat and pressure were applied to initiate an oxidation reaction, breaking down the potassium permanganate and depositing the manganese dioxide on lignin.

A prototype of the green supercapacitor made by Dr. Hong Liang’s team. (Credit: Dr. Hong Liang / TAMU Engineering)

Next, they coated the lignin and manganese dioxide mixture on an aluminum plate to form the green electrode. The supercapacitor was assembled by sandwiching a gel electrolyte between the lignin-manganese dioxide-aluminum electrode and another electrode made of aluminum and activated charcoal.

The supercapacitor showed stable electrochemical properties, with its ability to hold a charge changing little after thousands of cycles. Plus, the supercapacitors were both light and flexible.

“In this study, we have been able to make a plant-based supercapacitor with excellent electrochemical performance using a low-cost, sustainable method,” said Liang. “In the near future, we’d like to make our supercapacitors 100% environmentally friendly by incorporating only green, sustainable ingredients.”

Refilling Li-ion batteries
Researchers at Shanghai Jiao Tong University and Washington University in St. Louis are investigating a different way to recycle used lithium-ion batteries. Most battery recycling involves pulverizing it and separating the component materials.

Instead, the team is looking into electrochemical “refilling” of lithium-ion batteries into the spent electrodes to regenerate useful compounds, such as lithium cobalt oxide.

“Since 95% of the materials are still there and usable, we wanted to see if we could regenerate the complete lithium cobalt oxide compounds directly instead of recovering individual elements and then putting them together to be a useful compound,” said Zhen (Jason) He of Washington University in St. Louis. “We used an electrodeposition process where we deposited the lithium ions on the waste electrodes driven by the electricity that creates the electric field to absorb the ion onto the electrode.

“We can add an additional amount of lithium-ion into the waste electrode, and you get a complete formula that allows you to reuse those materials.”

In their feasibility study, the researchers were able to relithiate waste Li_xCoO₂ electrodes and restore the crystal structure with a post-annealing process. They plan to continue efforts to regenerate the materials in lithium-ion batteries and study its cost-effectiveness.