Saturday, December 25, 2010

Welcome To Graphene Supercapacitors

Curves are the key:
audiobytz - biweekly e-newsletter: "Building a test capacitor out of curved graphene sheets produced a device with an “specific energy density” of 85.6 Wh/kg (watt-hours per kilogram) at room temperature. A practical graphene battery would have a capacity of around 28 Wh/kg. Nickel-metal hydride (NiMH) batteries have an energy density of 40-100 Wh/kg, while lithium-ion batteries (used famously in PCs, cellphones, and MP3 players) top them both at 120 Wh/kg. But since NiMH or lithium batteries are often operated in the middle range of their discharge cycle, only 20 to 50% of their capacity is actually used. So a graphene capacitor “battery,” with the potential of being charged in seconds or minutes and which do not suffer from degradation upon recharging over possibly millions of cycles– they store energy electrostatically (by the accumulation of electrons) and not chemically – might become competitive for many applications. The illustration shows how the capacitance of the lab prototype (in farads/gram) varies – or, rather, hardly varies, over as many as 500 charge-discharge cycles. A typical chemical battery would have a detectable downward slope in as few as 100 cycles (hence the interest in iPod battery replacement)."