Lithium ion capacitor: Best of both worlds?

http://www.edn.com/index.asp?layout=blog&blog_id=1470000147&blog_post_id=1110030711
Monday, July 28, 2008
Lithium ion batteries, the current darling of the automotive world based on their potential for finally making electric vehicles practical, are not without drawbacks, a big one being their relatively limited cycle life. Anyone who’s experienced notebook battery capacity decline after a year or so of frequent charge-discharge cycling is familiar with this problem. Supercapacitors (aka, ultracapacitors), on the other hand, are great at cycling – 100,000 cycles with no degradation in capacity is common. Their Achilles heel is self-discharge: For many supercaps, sitting on the shelf for just a day or two is enough to significantly discharge them.JM Energy, an offshoot of the big materials vendor JS Micro, has announced a lithium ion capacitor with impressive specs: Energy density is 21-25 Wh/l, self-discharge of less than 5% after 3 months, and less than a 10% [thanks, Policbox] drop in capacity from initial after 100,000 cycles.Currently it comes in two series based on capacitance, one at 1100F and one at 2200F. JSE didn’t want to quote me a firm price, but they said a planning figure is about 10 cents/F.

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