The month in tech: A battery-free EV? (BBC)
An electric car, but where are the batteries?
The Quant e-Sportlimousine uses so-called “flow-cell” technology with two tanks filled with different liquid electrolytes to store energy. The liquid passes through a membrane in between the two tanks, creating an electric charge. The e-Sportlimousine emits no particulate or noxious emissions, has a claimed top speed of about 217mph and would accelerate from zero to 62mph in a Nissan GT-R Nismo-like 2.8 seconds. Nanoflowcell, its Germany-based builder, says the technology offers five times the energy capacity of lithium-ion batteries of the same weight, has no moving parts and contains no harmful substances. The car can travel 372 miles on a single charge and just earned a road-worthy approval on European roads.
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http://www.bbc.com/autos/story/20140801-the-217mph-electric-lab
http://en.wikipedia.org/wiki/Flow_battery
Well, this is a surprise, to say the least -- even proponents of flow-cell technology were saying that it was promising for stationary power storage, but didn't have the energy density for transportation applications. This is a very short blurb, so no details, but it seems they are in fact using the flow-cell as an all-liquid storage battery (never take journos' headlines too literally), rather than replacing the electrolyte to refuel as some have proposed. With retrospective wisdom* this does seem to make sense -- one of the problems with rechargeable solid and gel cells is a tendency for the regenerated electrode materials to form new crystals ("whiskers"
after several recharging cycles; eventually the whiskers bridge the electrodes, and recharging becomes impossible. With the redox couples being entirely in solution, the problem of physical restructuring of the electrodes vanishes, allowing more compact cell design, and the lifetime of the membrane most likely sets the limit on recharge cycles. One has to wonder, though, whether this is just a system which has reached its optimum design early; the active element is vanadium, which undergoes only one-electron redox at either electrode, and of course it's in solution, so the minimum bulk is high. Lithium-based cells seem capable of surpassing this in the long run, just based on the lower atomic weight of lithium.
*aka 20-20 hindsight.
= new reply since forum marked as read
... and I don't keep up with every new development in the technology. (If I did, I would probably not have been taken by surprise by the OP. ) I do know enough about general chemical principles (PhD in chemistry, albeit Organic) to be suspicious of some claims and encouraged by others, but I'm not sufficiently versed in the technical details to split the hairs too fine.
Evidently there's already been a lot of work done, by many groups, on various types of lithium-sulfur batteries. Note that several of the references in the Wiki are from 2013, so there may be several competing technologies reaching the market in the next several years. Some of these technologies strike me as a little esoteric, and not at all easy to manufacture, however.
Since these are room-temperature cells (unlike sodium-sulfur), I'm not sure exactly which safety issues concern you. Neither lithium nor sulfur is something you really want to catch fire, so there is the usual concern of overheating on charging faced by any high-energy-density device. Double the energy density, of course, and new problems are sure to crop up ... and multiple references to mechanical stresses caused by large changes in volume on discharging do make me cringe a little bit. I would assume that these devices would be tested out in applications with minimal civilian contact, say solar-charged telecom stations, remote sensor stations, RPVs, etc. for a year or two before being approved for more general use. It's definitely something interesting to watch, but I'm not expecting them to be incorporated into EV's any time very soon.
