Power/Performance Bits: July 15

Improving battery performance with sand
Researchers at the University of California, Riverside’s Bourns College of Engineering have created a lithium ion battery that outperforms the current industry standard by three times using sand as the key material.

The researchers, who said this is a low cost, non-toxic, environmentally-friendly way to produce high performance lithium ion battery anodes, are focused on building better lithium ion batteries, primarily for personal electronics and electric vehicles.

They are focused on the anode, or negative side of the battery. Graphite is the current standard material for the anode, but as electronics have become more powerful graphite’s ability to be improved has been virtually tapped out.

Because of this, researchers are now focused on using silicon at the nanoscale, or billionths of a meter, level as a replacement for graphite. The problem with nanoscale silicon is that it degrades quickly and is hard to produce in large quantities.

Schematic showing how sand is turned into pure nano-silicon. (Source: University of California, Riverside)

The improved performance could mean increasing the expected lifespan of silicon based electric vehicle batteries up to three times or more, which would be significant for consumers, considering replacement batteries cost thousands of dollars. The energy density is more than three times higher than that of traditional graphite based anodes, which means cell phones and tablets could last three times longer between charges.

The team is now trying to produce larger quantities of the nano-silicon beach sand and is planning to move from coin-size batteries to pouch-size batteries that are used in cell phones.

Getting a charge out of water droplets
When water droplets spontaneously jump away from superhydrophobic surfaces during condensation, MIT researchers discovered they can gain electric charge in the process and they’ve demonstrated that this process can generate small amounts of electricity that might be used to power electronic devices.

The researchers assert that this approach could lead to devices to charge cellphones or other electronics using just the humidity in the air; as a side benefit, the system could also produce clean water.

The device itself could be simple, consisting of a series of interleaved flat metal plates, the researchers said. Although initial tests involved copper plates, any conductive metal would do, including cheaper aluminum.

In initial testing, the amount of power produced was vanishingly small — just 15 picowatts, or trillionths of a watt, per square centimeter of metal plate. But the process could easily be tuned to achieve at least 1 microwatt, or millionth of a watt, per square centimeter and this output would be comparable to that of other systems that have been proposed for harvesting waste heat, vibrations, or other sources of ambient energy, and represents an amount that could be sufficient to provide useful power for electronic devices in some remote locations.

Making more efficient fuel cells
While solar power and other sources of renewable energy can help combat global warming, they have a drawback in that they don’t produce energy as predictably as plants powered by oil, coal or natural gas. Solar panels only produce electricity when the sun is shining, and wind turbines are only productive when the wind is brisk. Ideally, alternative energy sources would be complemented with massive systems to store and dispense power and reversible fuel cells have been envisioned as one such storage solution.

Fuel cells use oxygen and hydrogen as fuel to create electricity; if the process were run in reverse, the fuel cells could be used to store electricity, as well, according to researchers at Stanford University.

The electricity from wind or solar can be used to split water into hydrogen and oxygen in a fuel cell operating in reverse, noted William Chueh, an assistant professor of materials science and engineering at Stanford and a member of the Stanford Institute of Materials and Energy Sciences at SLAC National Accelerator Laboratory. “The hydrogen can be stored, and used later in the fuel cell to generate electricity at night or when the wind isn’t blowing.”

But like the renewable energy sources they need to complement, fuel cells have a drawback in that the chemical reactions that cleave water into hydrogen and oxygen or join them back together into water are not fully understood – at least not to the degree of precision required to make utility-grade storage systems practical.

However, Chueh is working with researchers at SLAC, Lawrence Berkeley National Laboratory and Sandia National Laboratories, and has studied the chemical reactions in a fuel cell in a new and important way.

The researchers have observed the hydrogen-oxygen reaction in a specific type of high-efficiency solid-oxide fuel cell and have taken atomic-scale “snapshots” of this process using a synchrotron particle accelerator. The knowledge gained from this analysis may lead to even more efficient fuel cells that could, in turn, make utility-scale alternative energy systems more practical.

The large red and white balls are oxygen atoms. The blue balls are hydrogen atoms. The arrow shows the fuel cell storing electricity during the daytime when the water molecule (left) lands its oxygen atom and surrenders two hydrogen atoms (blue balls at end of arrow). At night, the reaction would reverse. The two blue balls would pick up an oxygen atom and release the electricity they stored. The Stanford team discovered that the efficiency of the fuel cell depended on having empty spaces — or defects — on the fuel cell surface where oxygen atoms could land. (Source: Stanford National Accelerator Laboratory)