Power/Performance Bits: June 10

Cheaper, lighter solar cells
Think those flat, glassy solar panels on your neighbor’s roof are the best solar technology has to offer? Not so. Engineers in the University of Toronto’s Department of Electrical & Computer Engineering have designed and tested a new class of solar-sensitive nanoparticle that they say outperforms the current state of the art.

Based on a new form of solid, stable light-sensitive nanoparticles called colloidal quantum dots, solar cells made of this material could lead to cheaper and more flexible solar cells, as well as better gas sensors, infrared lasers, infrared light emitting diodes and more.

Collecting sunlight using these tiny colloidal quantum dots depends on both n-type and p-type semiconductors: the first rich in electrons, the latter poor in electrons. The problem is that when exposed to the air, n-type materials bind to oxygen atoms, give up their electrons, and turn into p-type.

However, the researchers have modeled and demonstrated a new colloidal quantum dot n-type material that does not bind oxygen when exposed to air.

Maintaining stable n- and p-type layers simultaneously not only boosts the efficiency of light absorption, it opens up a world of new optoelectronic devices that capitalize on the best properties of both light and electricity. For the average person, this means more sophisticated weather satellites, remote controllers, satellite communication, or pollution detectors.

How a lithium-ion battery works
New observations have revealed the inner workings of a type of electrode widely used in lithium-ion batteries and explain the unexpectedly high power and long cycle life of such batteries, MIT researchers say.

The electrode material studied, lithium iron phosphate (LiFePO4), is considered an especially promising material for lithium-based rechargeable batteries and has already been demonstrated in applications ranging from power tools to electric vehicles to large-scale grid storage. The MIT team found that inside this electrode, during charging, a solid-solution zone (SSZ) forms at the boundary between lithium-rich and lithium-depleted areas — the region where charging activity is concentrated, as lithium ions are pulled out of the electrode.

The diagram illustrates the process of charging or discharging the lithium iron phosphate (LFP) electrode. As lithium ions are removed during the charging process, it forms a lithium-depleted iron phosphate (FP) zone, but in between there is a solid solution zone (SSZ, shown in dark blue-green) containing some randomly distributed lithium atoms, unlike the orderly array of lithium atoms in the original crystalline material (light blue). This work provides the first direct observations of this SSZ phenomenon. (Source: MIT)

The observations help to resolve a longstanding puzzle about LiFePO4: In bulk crystal form, both lithium iron phosphate and iron phosphate (FePO4, which is left behind as lithium ions migrate out of the material during charging) have very poor ionic and electrical conductivities. Yet when treated — with doping and carbon coating — and used as nanoparticles in a battery, the material exhibits an impressively high charging rate.

The researchers conclude that these findings provide convincing and direct evidence of the mechanism at work and is a major step forward for pushing the ambiguities toward favoring a solid solution model.

Power storage in a single wire
Imagine being able to carry all the energy needed to power an MP3 player, smartphone and electric car in the fabric of a jacket. While it might sound like science fiction, it may become a reality thanks to researchers at the University of Central Florida.

Today, electrical cables are used only to transmit electricity but the team at UCF have developed a way to both transmit and store electricity in a single lightweight copper wire.

Copper wire is the starting point but eventually as the technology improves, special fibers could also be developed with nanostructures to conduct and store energy, the researcher said.

More immediate applications could be seen in the design and development of electrical vehicles, space-launch vehicles and portable electronic devices. By being able to store and conduct energy on the same wire, heavy, space-consuming batteries could become a thing of the past. It is possible to further miniaturize the electronic devices or the space that has been previously used for batteries could be used for other purposes. In the case of launch vehicles, that could potentially lighten the load, making launches less costly, they said.