Lithium-ion capacitor combines more than 100,000 charge cycles, low self-discharge rate
By Margery Conner, Technical Editor -- EDN, July 31, 2008
Lithium-ion batteries are the current darlings of the automotive world because of their potential for finally making electric vehicles practical. They are not without their drawbacks, however, including their relatively limited cycle life. This problem affects notebook computers, which typically experience battery-capacity decline after a year or so of frequent charge/discharge cycling. Supercapacitors, on the other hand, provide 100,000 cycles with no degradation in capacity. They, too, have an Achilles’ heel, however: Leaving them on the shelf for just a day or two can cause them to self-discharge.
JM Energy has now come up with an approach that combines the best features and omits the flaws of both these technologies. The company, an offshoot of petrochemical company JSR Corp, has announced a lithium-ion capacitor with energy density of 21to 25 Whr/l, self-discharge of less than 5% after three months, and less than a 10% drop in capacity from initial charge after 100,000 cycles. The units’ voltage ranges from 2.2 to 3.8V. The 1000F series has a capacitance of 1100F and an internal dc resistance of 2.5 mΩ; the 2000F series has 2200F capacitance and an internal dc resistance of 1.4 mΩ. JM Energy plans to offer the devices for approximately 10 cents per farad.
