Japanese Aim for Tenfold Gain in Capacitor Power

Advanced Battery Technology,  Oct 2004  

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Omron has teamed up with Mitsui, Okamura Laboratory, and Power Systems to develop ECaSS technology that could deliver energy densities of 60Wh/l by 2005, ten times the energy of existing devices.

If Omron can deliver such a density it would allow supercapacitors to eat further into the secondary battery market. NiMH and lithium-ion cells have densities in the order of 100Wh/l.

Unlike batteries, supercaps cannot be overcharged, require no special charging circuits, and can be soldered directly to PCBs. They do not convert energy using a chemical conversion and can be recharged and discharged in seconds.

Also known as electrical double-layer capacitors, supercapacitors are formed from layers of activated carbon and a liquid electrolyte. Positive and negative charges distribute themselves in opposition to each other in boundary layers. Stored charge can be huge, as even a gram of carbon can have a surface area of thousands of square meters due to pores in the carbon.

However, the devices have quite low breakdown voltages, and relatively high (tens of milliOhm) internal resistances means they can only be used in DC circuits.

Omron said activated carbon has reached its practical limit, as no more pores can be made in the material. To take supercapacitors to 60Wh/l, the consortium will use what it calls a "nanogate" capacitor in which ions in the electrolyte form pores in the carbon.

Meanwhile, Maxwell Technologies of San Diego, California, has introduced a D cell-sized supercapacitor rated at 350 Farads and 2.5V. The energy density is claimed to be 21 Joules/cm^sup 3^, which corresponds to around 6Wh/kg.

Copyright Seven Mountains Scientific, Inc. Oct 2004
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