February 18, 2010

Intel lab researching dielectric coatings for nanocapacitors for nanoscale power storage

EETimes reports that Intel researchers are exploring nanoscale materials that could be used to create ultracapacitors with a greater energy density than today's lithium ion batteries. If successful, the new materials could be mass produced in volumes to power systems ranging from mobile devices to electric vehicles—even smart grid storage units.

The lab is focused on so-called microgrids, small local electric grids that lab director Tomm Aldridge and others believe could represent the future of the smart electric grid.

"It's way too early to announce any results, but we are taking what we think is a fresh look at building ultracapacitors using our expertise in nanomaterials fabrication and high volume manufacturing," said Aldridge. "The research targets are to exceed energy storage of battery technology in terms of energy density and figure out how to assemble these nano-capacitors into ultracapacitors that have useful voltage ranges," he added

The energy-storage effort is exploring use of engineered dielectric coatings to create the capacitors that could be scaled to large arrays. MIT, Stanford and other universities are also exploring nanoscale ultracapacitors as a medium as an alternative with longer life time and more resilience to harsh conditions than traditional batteries.

MIT Technology review discussed similar research in 2009 at the University of Maryland

Researchers at the University of Maryland have developed a kind of capacitor. The research is in its early stages, and the device will have to be scaled up to be practical, but initial results show that it can store 100 times more energy than previous devices of its kind.

Sang Bok Lee, a chemistry professor, and Gary Rubloff, a professor of engineering and director of the Maryland NanoCenter, created nanostructured arrays of electrostatic capacitors. Electrostatic capacitors are the simplest kind of electronic-energy-storage device, says Rubloff. They store electrical charge on the surface of two metal electrodes separated by an insulating material; their storage capacity is directly proportional to the surface area of these sandwich-like electrodes. The Maryland researchers boosted the storage capacity of their capacitors by using nanofabrication to increase their total surface area. Their electrodes work in the same way as ones found in conventional capacitors, but instead of being flat, they are tubular and tucked deep inside nanopores.

The fabrication process begins with a glass plate coated with aluminum. Pores are etched into the plate by treating it with acid and applying a voltage. It's possible to make very regular arrays of tiny but deep pores, each as small as 50 nanometers in diameter and up to 30 micrometers deep, by carefully controlling the reaction conditions. The process is similar to one used to make memory chips. "Next you deposit a very thin layer of metal, then a thin layer of insulator, then another thin layer of metal into these pores," says Rubloff. These three layers act as the nanocapacitors' electrodes and insulating layer. A layer of aluminum sits on top of the device and serves as one electrical contact; the other contact is made with an underlying aluminum layer.

In a paper published online this week in the journal Nature Nanotechnology, the Maryland group describes making 125-micrometer-wide arrays, each containing one million nanocapacitors. The surface area of each array is 250 times greater than that of a conventional capacitor of comparable size. The arrays' storage capacity is about 100 microfarads per square centimeter.

Digital quantum batteries could have ten times the energy storage of lithium batteries. Capacitors built as nanoscale arrays--with electrodes spaced at about 10 nanometers (or 100 atoms) apart--quantum effects ought to suppress arcing between electrodes. the energy density and power density in nano vacuum tubes are large compared to lithium batteries and electrochemical capacitors. The electric field in a nano vacuum tube can be sensed with MOSFETs in the insulating walls.

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