Power/Performance Bits: Oct. 6

Portabella batteries

Researchers at the University of California, Riverside created a new type of lithium-ion battery anode using portabella mushrooms, which are inexpensive, environmentally friendly and easy to produce. The current industry standard for rechargeable lithium-ion battery anodes is synthetic graphite, which comes with a high cost of manufacturing because it requires tedious purification and preparation processes that are also harmful to the environment.

UC Riverside engineers were drawn to using mushrooms as a form of biomass because past research has established they are highly porous, meaning they have a lot of small spaces for liquid or air to pass through. That porosity is important for batteries because it creates more space for the storage and transfer of energy, a critical component to improving battery performance.

In addition, the high potassium salt concentration in mushrooms allows for increased electrolyte-active material over time by activating more pores, gradually increasing its capacity.

Schematic illustration of the process of obtaining Portobello mushroom skin-derived, hierarchically porous carbon nanoribbons used as free-standing, binder-free, current collector-free carbon anodes. (Source: Lauro Zavala/UC Riverside)

A conventional anode allows lithium to fully access most of the material during the first few cycles and capacity fades from electrode damage occurs from that point on. The mushroom carbon anode technology could, with optimization, replace graphite anodes. It also provides a binderless and current-collector free approach to anode fabrication.

The nano-ribbon-like architectures transform upon heat treatment into an interconnected porous network architecture which is important for battery electrodes because such architectures possess a very large surface area for the storage of energy, a critical component to improving battery performance.

Going vertical

Materials scientists at UCLA created an improved structure for one type of organic semiconductor, a building block of a conductive polymer called tetraaniline, showing for the first time that tetraaniline crystals could be grown vertically.

The discovery could eventually lead to improved technology for capturing solar energy, reshaping solar cells to create “light antennas” — thin, pole-like devices that could absorb light from all directions.

The UCLA team grew the tetraaniline crystals vertically from a substrate, so the crystals stood up like spikes instead of lying flat as they do when produced using current techniques. They produced the crystals in a solution using a substrate made of graphene. Scientists had previously grown crystals vertically in inorganic semiconducting materials, including silicon, but doing it in organic materials has been more difficult.

A scanning electron microscopy image of a vertical tetraanaline semiconductor crystal. (Source: Jessica Wang/UCLA)

Once the team found they could guide the tetraaniline solution to grow vertical crystals, they developed a one-step method for growing highly ordered, vertically aligned crystals for a variety of organic semiconductors using the same graphene substrate.

Richard Kaner, professor of chemistry and biochemistry and materials science and engineering at UCLA, said the researchers also discovered another advantage of the graphene substrate.

“This technique enables us to pattern crystals wherever we want,” he said. “You could make electronic devices from these semiconductor crystals and grow them precisely in intricate patterns required for the device you want, such as thin-film transistors or light-emitting diodes.”