• Mar 12th 2009 at 4:58PM
  • 8
Researchers at the Massachusetts Institute of Technology have been researching where the bottlenecks are inside lithium-ion batteries that limit charging and discharging rates, and they've learned some interesting things. Lithium iron phosphate chemistry is particularly promising in terms of high charge and discharge rates. Researchers found that some new processes for manufacturing the lithium phosphate coating on lithium iron phosphate crystals could provide better access to the lithium ions, allowing them to move around more readily.
This all sounds similar to the premise behind the lithium iron phosphate batteries produced by A123 Systems and the lithium titanate cells produced by Altairnano. The increased surface area of material allows more ions and electrons to move in and out without heating up as much as traditional lithium cobalt oxide cells. The result is that cells made with these materials can be charged at very high rates without degrading the charge capacity over time. Imagine charging your electric vehicle in two minutes rather than 12 hours and you can understand the significance of this research.

The bigger issue remains the power needed to actually charge an automotive sized battery pack in a few minutes. A five-minute charge would require 180 kW or more, which is not something that's available at home or any existing charging stations.

[Source: ars technica]

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    • 1 Second Ago
      • 6 Years Ago

      Obviously Sam Abuelsamid never excelled in math. In the first place, 5 minute
      recharges are silly - it will be more like 10 to 15 minutes. And a 5 five minute recharge at 180kws is only going to pump (at most) 1/12th of 180 , or about 15 kilowatthours into any battery, which is less than 75 miles of travel for all but the tiniest of EVs.
      And he couldn't have meant 1800kws, either. So old Sam is wrong in all directions. Also, a 180kw pipe is no big deal, unless you
      are talking about household capacities, but why do you care about that? recharges at the home can proceed with your typcial 220V/50A feed, pumping out 11 kilowatts,enough to recharge a 50 kilowatt battery from zero (with a 250 mile driving range) in 4 1/2 hours. And how often do you need to recharge that fast, that much? If you do, then stop by your local recharge station, which has a big feed and can recharge at 10 minute rates. Sam is obviously much confused about recharging hows and wheres.
      Just do a little thinking Sam, before you start typing. Works out better that way.
      It's obvious that 1) most redcharges will be done at home, and there is no crying need to do full recharges in less than 5 hours, or 55 minutes for 50 mile 's worth of juice. The need to do recharges is primarilly for 1) those who have no ability to recharge either at home or during work (when recharge time is mostly irrelevant) 2) those on a trip.
      Got that, Sam?
      • 6 Years Ago
      To say that "the bigger issue remains the power needed to actually charge an automotive sized battery pack in a few minutes" is just ignorant. Electrical infrastructure is in place and can be expanded with minimal effort, compared to the challenges associated with actually developing new high specific-power / specific-energy long-life batteries. Go to school!
      • 6 Years Ago
      If I remember well current hybrids regenerative breaking is very inefficient because the battery can't charge fast enough to store all the energy which could be retrieved from the braking.
      Faster charging battery would also benefit non plugged in hybrid cars by wasting less energy as heat in the brakes
      • 6 Years Ago
      You need a big pipe, but
      1. you rarely need to fast charge at home anyway (charge overnight)
      2. there are existing industrial chargers that could handle this (400v or higher) that could be installed at "charging stations" wherever those may end up
      3. fast chargers can use huge sets of capacitors so that they can charge themselves up more slowly from the grid and "dump" their charge into a fast charging battery faster than the grid can provide it (and capacitors are 99% efficient so there isn't a huge loss to enable this functionality)

      We keep hearing about this type of nano-engineered lithium technology and there are some out there (A123, Altair Nano), but wide-scale production just isn't getting off the ground... cost is supposed to be the same or lower in most cases, so it seems like they just haven't figured out how to get very high yields yet... something this good will be stuck in prototype for many years.
        • 6 Years Ago
        The problem with using capacitors like this is the size, however with these quick charge/discharge batteries you could use them instead of the capacitors as the power density is better.

        180kW*5min=15kWh thats kinda small for a car battery, wasn't Phoenix truck supposed to have like 35kWh and the Tesla is supposed to be 53kWh which in 5 minutes is 636kW, just charging two at once requires more than a megawatt service. Also since the Tesla stores its power at ~375V that is ~1.7kA talk about ohmic losses. Also this also gets lots worse if you want to go faster a 2.5 minute charge will take that ~1.3 megawatt connection.

        Anyway it looks like the electric economy is a ways out there still.
        • 6 Years Ago
        My point was that the charging station has the capacitors/supercapacitors/ultracapacitors inside so you don't need a megawatt of service (they charge gradually off the grid like a defibrillator does, once the capacitors are full then they can dump their charge into your EV at a much higher rate than the mains power alone could handle). As long as there are a few minutes before the next EV comes for a charge, there would be time for the capacitor to fill up (you could even have "ready/charging" indicator lights on the charging stations so you can pull up to one that's ready). You could use these fast charge batteries in the charging station, but dumping grid->battery->battery is a bit less efficient than dumping grid->capacitor->battery... not to mention the volume/energy density/weight of the charger is much less important than for the battery in an EV, as well as capacitors being more durable for MANY cycles (millions). Think of gas stations that have huge underground tanks, why not have a charging station with huge underground vaults with banks of capacitors?

        If the capacitor in the charging station is empty before your EV is charged, you could continue charging off 400v+ mains power (at a slower rate) for a few minutes (and could unplug early if your EV indicates enough estimated miles remaining to get to your destination), but if such a charging station were built they would probably use capacitor banks with much larger energy capacity than most car batteries.
      • 6 Years Ago
      That makes sense...

      Electric charge travels over the surface of things, not nearly as easily going through them. The electrical charge capacitance probably gets drawn in from the surface into the interior of the chemical cell.

      Tunnels increase surface area, and provide surface access into the interior of the cell.

      The C-rating of these batteries (rate of how many amps or milli-amps per hour the battery can discharge) will skyrocket if the surface area allows surface flow of electrons into and out-of the interior of the battery.

      The charging rate is directly related to the discharge rate, and most lithium batteries like to stay near 1 times C, although some are force-charged faster, up to 3 or 4 times C. Force-charging also depletes the batteries faster by damaging the chemicals.

      Instead of charging at multiples of the batteries discharge rate, increasing the discharge rate is fantastic, because it also affects charging rate...

      I wonder if they can make the leap from a solid-block cell, to a perforated cell, like this describes, to an open-celled sturdy foam structure, with even more surface area, with a modest amount of physical growth due to inert air-space, (can't be oxygen, because lithium oxidizes explosively.) or some sort of liquid saturated foam, to allow electrons to flow throughout the cell almost instantaneously, with much less thickness per square inch of surface area.

      This is very promising stuff.

      One step closer to my turboshaft jet/electric hybrid-drive supercar idea. :D
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