The Economist searches for the perfect vehicle battery
Many of you out there are pretty knowledgeable about the batteries used in today's hybrids and electric cars. I am not. Sure, I've read thousands, nay, million of words about them. I can even recognize the scientific names of the more common chemistries such as LiFePO4 which stands for lithium, iron and potatoes. Ok, so I don't quite have the chemistry thing quite nailed down. Luckily for me, and people like me, there are articles being written that not only help us understand how these things work but also give a historical perspective and a heads up about what people are working on now.
One such essay has just appeared in The Economist, a somewhat opinionated but respected British weekly, under the title, "In search of the perfect battery." In their quarterly report on technology, the Economist breaks down, in language even I can understand, how a modern lithium cell works (and why some explode). The history of li-ion is discussed as well as the state of the present quest for the holy battery grail. I recommend you give it a read so you, too, can know your anodes from your potatoes.
[Source: The Economist]
Reader Comments (Page 1 of 1)
KarenRei 6:48PM (3/10/2008)
Here's my collection of interesting next-gen battery techs. Feel free to suggest more techs or any corrections:
http://www.daughtersoftiresias.org/greenwiki/Electric_vehicle#Charge_time
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Conventional lithium ion laptop batteries are generally around 160Wh/kg and 270Wh/L using a lithium cobalt oxide cathode and a graphite anode. Among the many new anode/cathode combinations[6] are:
Lithium iron or magnesium phospate cathodes, like A123s "nanophosphate": Many companies are taking this route. Fast charge (when nanophosphate-type), long life, safe, expected to be reasonably cheap when produced in volume. "Methanol" method of adding carbon support expected to make them quite cheap. GS Yuasa corp demonstrated 156Wh/L and 108Wh/kg with a graphite anode.
Toshiba's SCIB: Unknown tech. Fast charge, long life, safe, ~80% of the energy density, reportedly reasonably cheap
Hybrid Technologies' "superlattice" manganese-cobalt-nickel-titanium cathode: An amazing 936Wh/kg is claimed, although given the stats cited for other li-ion types, it seems this is for the cathode alone (about a 2x improvement over LiCoO2). The cathode material is reportedly already produced at an industrial scale, and allows for a wide range of possible voltages per cell. Fast charge/discharge reported.[7]
Titaniate anodes, like AltairNano's: Fast charge, long life, safe, slightly lower voltage, 100Wh/kg. Currently expensive ($2/Wh), reportedly due to limited production.
Lithium vanadium oxide anode, such as Samsung's prototype: 695Wh/L when paired with a traditional LiCoO2 cathode, boosted to 745Wh/L by vapor deposition of a Li metal film. Slightly lower expansion than a graphite anode, suggesting longer life. 80% capacity after 500 cycles (not as much of a problem with high energy density batteries, as you go farther on a cycle). Subaru's prototype G4e uses such a battery, and is capable of fast charging.[8]
Silicon carbon composite anode, such as the Hitachi/Sanyo prototype: Silicon anodes hold a tremendous amount of lithium -- typically too much, causing them to swell and fracture. Uses PVDF to help bind the anode to ameliorate the loss as the silicon fractures. Only gets 70% capacity after 200 cycles.
Silicon/copper foil anode, such as the Hitachi/Sanyo prototype: Similar, but uses a copper foil to retain the cracking silicon. 60% capacity after 200 cycles, with a 40% increase in energy density.
Silicon nanowire anode, such as the Stanford/Yi Cui prototype: Uses nanowires on a stainless steel substrate to avoid silicon cracking altogether. 10x the lithium absorption on the first charge, 8x on subsequent charges, leading to "several" times the energy density without a cathode improvement and the full improvement with a corresponding cathode advance. 1000-cycle validation expected by summer of 2008, and commercialization expected in five years, with a cost cheaper per Wh than conventional li-ion.
Li-ion isn't the only game in town. Lithium-sulphur batteries offer 250Wh/kg. Sodium-ion batteries promise 400Wh/kg with only minimal expansion/contraction during charge/discharge and a very high surface area (fast charge/discharge). The list keeps on going; there are a lot of interesting new battery chemistries trying for a share of the market. Additionally, EEStor's EESU ultracapacitor is scheduled to hit the market in early to mid 2008, also with a rapid charge time (4-6 minutes) at 342 Wh/kg and 1600Wh/L[9]. Conventional ultracapacitors making use of carbon nanotubes to increase surface area are also competitors[10]. Finally, an alternative to fast charging stations is battery replacement. While it suffers from some problems (weight, standardization, etc), Project Better Place has already raised several hundred million dollars to build networks of charging and battery replacement stations. One type of battery "replacement" proposed is much simpler: while the vanadium redox battery only has an energy density similar to lead-acid, the charge is stored solely in a vanadium-based electrolyte, which can be pumped out and replaced with charged fluid.
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