5408Re: [evworld] Re: Batteries
- Oct 8, 2005Hi 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:
At 07:30 PM 3/29/2004, Paul Scott wrote:
A question for you engineers on the lists. This is a quote from "Power To
the People" by Vijay Waitheeswaran in a section on the battery electric
"The trouble is that battery systems are pushing the upper limits of
specific energy - the number of watt-hours they can store for a given
weight. The best that conventional batteries can achieve theoretically is
300 watt-hours per kilogram (Wh/kg), though most manage barely half that in
practice. That is nowhere near enough for the armed forces. The Pentagon has
said that it wants to deploy portable equipment loaded with energy-guzzling
features that would require up to 3100 Wh/kg by 2006. The physical
properties of batteries make it impossible for them to ever achieve such
His comments on the needs of the military notwithstanding, are his facts
and figures correct on the battery's theoretical limit? I had not heard of
such a limit and he doesn't explain it at all.
This does remind me of gloom and doom anti-technology predictions from
the past. It is possible to know and calculate the theoretical maximum
energy from specific battery combinations---that's basic electrochemistry.
The theoretical limits of current batteries are actually much higher than
300 wh/kg. The basic reactants of lead acid imply a limit around 120
watt hours per kilogram, and actual batteries deliver 20 to 40 wh/kg.
At the other extreme, I believe the reactants of current lithium battery
chemistries imply a theoretical value around 1500-3000 wh/kg. The
difference between the theoretical and actual values results from the
weight of case, electrical conductors, separators, electrolyte, important
non-reactant ingredients, and reactants that don't get used.
Fifteen years ago, the best practical and known rechargeable batteries
delivered maybe 70 wh/kg. Today, commercial batteries are reaching
200 wh/kg. It is fair to argue on a technical basis that a specific
chemistry will have a definite practical performance limit. But new
combinations will continue to be developed in the future; I wouldn't
want to predict where things will go in the future. I certainly wouldn't
want to predict that technology won't improve beyond a certain point.
I can't see what practical applications would need 3000 wh/kg.
> All good points Ernie. To look at electric vehicles today, one would think
> they all have
> to be small and extremely ugly. Also looking at hybrids and plug-in
> hybrids gives the
> impression that we will always have an internal combustion engine in our
> vehicle. But
> predicting the future can make everyone look silly.
> For now, the plug-in hybrid looks like the best "vehicle" to blaze the
> trail to a pure
> electric vehicle. Biofuels definitely fit well with a plug in hybrid and
> hopefully we
> will see both these technologies blossom soon. With the history of battery
> vehicles, it's easy to understand why they seem limited to small marginal
> units. But
> every single limitation of the battery electric vehicle that I've been
> able to think of,
> all leads back to the battery. The next question one must ask oneself is,
> has battery
> technology already reached its zenith. If we listen to General Motors and
> others, this is
> the case. They claim that they've given up on the battery and have moved
> on to the
> hydrogen fuel cell. What they actually claim is that they've given up on
> the electric
> vehicle, but we all know a hydrogen fuel cell vehicle is nothing but an
> electric vehicle
> that gets its electricity from the fuel cell.
> Possibly the battery has run up against a technological brick wall.
> Possibly General
> Motors is being genuine and does not have a hidden agenda in their
> campaign to explain to
> us why they have given up on the battery electric vehicle. But while
> General Motors and
> US Car may have given up, others still have some hope for the battery. My
> belief is that
> battery technology is still in its infancy. Materials science along with
> growing need
> from all sectors of society may still produce some very pleasant and
> exciting battery
> technology surprises for us in the future.
> Why should a battery be any different than the gas tank? Why can't a
> battery be superior
> to a fuel tank? If the battery can be recharged in about the same amount
> of time it takes
> to fill the fuel tank, that eliminates one of the biggest gripes. If the
> battery can be
> made to work in all weather conditions, another common gripe goes by the
> wayside. And if
> range can be achieved similar to that of liquid fuel vehicles, no one will
> have that to
> complain about. There or still cost and environmental and other issues to
> consider but I
> see no brick wall.
> Why couldn't a large truck be a pure battery vehicle? What, other than our
> perceptions or misperceptions makes something like this impossible. It's
> tough to twist
> our minds in new ways and as we predict the future were sure to look like
> fools at times.
> There is also a lot of inertia to break through, as with any new concept.
> The electric
> vehicle is generally understood to have certain characteristics. Even
> people who are
> usually up on the latest technologies and are knowledgeable about vehicles
> in particular
> will often hold some very incorrect views about electric vehicles. Battery
> trucks may still be a long way off but the view of all electric vehicles
> as being slugs
> on the road is about to be shattered.
> The Toyota Prius is a very neat car and has obviously made a huge splash.
> But a muscle
> car or a sports car it's not. But with the Lexus hybrid SUV we are seeing
> the beginnings
> of what electric drive can do to enhance performance. With the Lexus 450H,
> the perception
> of electric drive as being inherently slow will be confronted directly. It
> won't take too
> long for people to put two and two together and realize that electric
> motors are not only
> the best way but by far the fastest way to move the vehicle. As
> perceptions change, so
> will products. For now our best bet to help things move along is to
> promote the plug-in
> hybrid electric vehicle, "the gateway vehicle" as Murdoch has so cleverly
> put it. Beyond
> that we need to keep our minds open for much better things to come.
> Because electric
> motors are the best choice for powering big trucks for the same reasons
> they are the best
> choice for powering locomotives and other machinery. It's just a question
> of how we're
> going to get the electricity to them.
> --- Arcologic@... wrote:
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