Re: Battery breakthrough

From: sanman (manofsan_at_yahoo.com)
Date: 11/05/04 

Date: 4 Nov 2004 17:07:07 -0800

Evgenij Barsukov <evgenij_b_no_spam@yahoo.com> wrote in message news:<cmdi2j$qa2$1@home.itg.ti.com>...
> Interesting work and coming from a respectable group. I agree that more
> should be done with Al, because it can eventually work in water rather
> then in organic electrolytes as Li-ion battery does. But energy density
> (not coulomenric!) will never reach Li-ion because of its much higher
> activity (=higher cell voltage).
>
> Now, about nanocrystalline. If I hear that, my first thought are
>
> 1) high surface area = high self discharge. This is always true with
> batteries involving high energy materials that are only stable because
> of insulating layers on the surface.
>
> 2) Nanocrystalline matterials have small particles therefeore more
> contact area between particles. This means lower overal conductivity
> and more problems - because loss of electrical contact between particles
> is a huge issue even with relatively large 10-50mkm particles used
> in Li-ion. If you go to even smaller particles, accumulation of
> decomposition products on their surface will disconnect them even earlier.
>
> 3) Finaly, the very need to go to small particle size indicates
> that cristalline structure of material itself is not sufficiently
> open for intercalation and therefore you are forced to use higher
> surface area (with above mentioned problems). So, as a general direction
> I would always try to find a cristall with more open structure (like
> iron phosphates, for example) rather then going nano - for any
> practical battery.

Hmm, I read once about some Lithium-Iron-Phosphate compound being used
to make a highly conductive electrode.

> That basicaly supports my point 2. I would say, voltage drop
> over the cathode material is a large problem.
> As for redox potential, it is always defined by potential
> of both cathode and anode.

I once read about carbon nanotubes being mixed in with photovoltaic
semiconductor material, in order to exploit the higher conductivity of
the nanotubes, so as to more efficiently transport current.

>
> >
> > If you look at the V2O5 graph (using silver extrapolated to lithium
> > ions?), it shows a maximum of 275 mAh/g, which would be ~400 Wh/kg?
> >
> > So is aerogel or nano-foamed metal now being used to exploit
> > Aluminum's energy density?
>
> More likely Al3+ is not able to penetrate V205 cristall and
> is deposited mostly on the surface, hence the need for nanocristalline
> structure. But as result of this, only a fractioni of full intercalation
> capacity of this material is used.

Hmm, so the ideal configuration at atomic level would be nearly like a
3D checkerboard to have maximum Al3+ and V2O5 contact. Hmm, perhaps
one day?

> Al3+ is expected to perform worse then Li+ because
> 1) Li+ is much smaller so can more easily intercalate
> 2) Li->Li+ couple has higher potential then Al
>
> Regards,
> Evgenij

So does that mean that theoretically Li has the best prospects out of
any possible ion?
I was reading about Koreans examining possibly polymers and even
multiwall carbon nanotubes.

Could multiwall carbon nanotubes allow for intercalation of cations in
between the walls? What about single wall nanotubes?
The nanotubes seem to have fabulous conduction properties, which would
be nice for higher power output.

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