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5411Re: [evworld] Re: Batteries

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  • murdoch
    Oct 8, 2005
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      On Sat, 8 Oct 2005 10:57:14 -0800, you wrote:

      >Hi All,
      >I'm enjoying the talk about batteries. Yes, it's the crux of the matter. A
      >while back, I asked a question to the EV lists about the theoretical limits
      >to batteries. I got several great responses, but William Kortoff's seemed to
      >be the best. I'm reprinting it below:

      To some extent, I think some of the stumbling-in-the-dark we are doing
      in trying to bring ourselves up to speed on batteries is not just how
      fast this nascient industry is moving, or can move, but also that we
      live in these bizarre times where, taken as a whole, our (U.S.)
      country's industries and media and government and some populace are
      resisting progress and enlightenment when it comes to technologies
      that can help obsolete our oil addictions.

      That said, these wh/kg barriers are something we should definitely
      discuss more. I wish I knew more, such as by attending a conference
      that could help bring me up to date.

      One somewhat-outdated-but-perhaps-still-slightly-useful perspective is
      available as part of this group's files here:


      Note that it was prepared for CARB in 2000, and as it ages, it's
      interesting to look back on it, as something you've sort of paid-for,
      and see how its conclusions hold up.

      A top industry person mentioned to me one of these thresh-holds, I
      think it was 300 wh/kg for Lithium based batteries, in terms of trying
      to devise aerial vehicles. It's been far too long since I looked at
      relevant charts (I'm sure others will come up with some good links for
      us) but as we continue to make the reasonably-expected-progress on
      better "advanced" batteries, these previously-difficult numbers start
      to look perhaps reachable. If we go back a few years, it always
      seemed like there was a "catch" to the batteries with better energy
      density per unit mass.

      William responds to you:

      >I can't see what practical applications would need 3000 wh/kg.

      How about "any"? Isn't there some famous quote from Bill Gates not
      seeing how anyone would need more than 640K of RAM?

      If we specifically look at the aerial applications issue, and how the
      US Military has apparently gone somewhat out of its way to deal with a
      more advanced battery such as Aerotech's, we can see how the energy
      per unit mass issue becomes critical and nearly impossible to put
      limits on the benefits of improving the number. If we ever want to
      dare to think of moving some aviation away from the present
      technology, we'll need to think big with a lot of different
      technologies, not just batteries (and let's not forget that ACP's
      Li-Ion tzero came about in part due to batteries that were being used
      by model airplane enthusiasts).

      Since weight is such a critical element in getting better mileage with
      vehicles, I think any improvements we can make in weight with
      batteries are something I look for.

      When I hear "zinc-air", even though I don't think they're always
      rechargeable so much as "rebuildable", I think that maybe some of the
      "fuel" is being carried outside the vehicle itself (just as an IC
      engine uses mass that is from outside (Oxygen combusted with

      With conventional vehicles, the fuel weighs something (6-8 pounds per
      gallon?) and the powertrain weighs something. Manufacturers have been
      in earnest seeking powertrain weight improvements and generally
      nowadays advanced engines often seem to incorporate some sort of
      aluminum alloy. Likewise, the non-powertrain-relevant aspects of the
      car also employ weight-saving measures in some more advanced cars. One
      car that stood out about 10 years ago was the original Acura (Honda)
      NSX in terms of its use of Aluminum in the frame, and not just in some
      more conventional areas. Likewise, some of the recent public-policy
      organizations, that are pushing for better-mileage vehicles in terms
      of how they can help us all on various fronts, have started mentioning
      such issues as bringing more carbon-fiber focus to bear and lowering
      the weight of vehicles.

      When I think of the specific-energy-by-mass limitations on batteries,
      I think about the challenge of creating a charge differential and
      holding it and then delivering current to power something. A certain
      number of protons and neutrons would appear to be necessary and so it
      has always seemed somewhat logical that a Lithium-based approach
      (incorporating a lighter-weight element) might hold promise for saving
      weight. Obviously, we're going to go through a lot more innovation
      than that over the next few centuries in this field and others that
      are related.

      Maybe we should think about developing some of our own data, if none
      is conveniently available, though surely there must be some good stuff
      around. Just for the heck of it, I'd be curious to see how mechanical
      springs stack up (yes, mechanical springs), as well as some of the
      other technologies that some group participants often ask that we not
      leave out of the discussion, such as compressed air, hydraulic energy
      storage, boron, Hydrogen (there must be some fans amongst us) etc.
      Some of these are conventional "fuel-users" though, whereas with a
      battery or a spring or something, the onboard-mass does not change as
      the vehicle is fueled-up or down.

      I guess my last thought for now is that at some point one of the
      better Lithium cars was mentioned as storing 50 kWh and this is a lot.
      That's still less than half a gallon of gasoline, in terms of energy
      content, or maybe about 25 times less than what we might find in an 11
      gallon fuel tank. I agree with absolutely not shutting the door on
      making progress in this area, but it is useful to know what we are up
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