
Batteries that “drink” seawater could power long-range underwater vehicles - yurisagalov
http://news.mit.edu/2017/batteries-drink-seawater-long-range-autonomous-underwater-vehicles-0615
======
wpietri
My chemistry's weak, but isn't this basically a way to extract the energy put
in when aluminum is refined? A quick internet search suggests that's 75
KWh/kilo. Lithium Ion batteries are apparently 0.2 KWh/kilo, so even assuming
a lot of loss in refining and then "burning" the aluminum, it seems plausible.

~~~
whatshisface
Well, it's absolutely the case that seawater isn't fueling it.

Edit: Removed incorrect speculation. Sorry, HN.

It turns out that they actually are using the water - in the same way that an
IC engine would breathe air.

If fuel cells aren't batteries, I wonder if this is still one?

~~~
gizmo686
Based on the article's description, the water is a part of the main chemical
reaction. It sounds like the reaction (essentially) H20 + Al -> H2 + Al(OH3),
with an unspecified alloy of alluminum.

------
donquichotte
Aluminium batteries are interesting and may be promising. According to
Wikipedia, in 2002 Yang and Knickle concluded:

 _The Al /air battery system can generate enough energy and power for driving
ranges and acceleration similar to gasoline powered cars...the cost of
aluminium as an anode can be as low as US$ 1.1/kg as long as the reaction
product is recycled. The total fuel efficiency during the cycle process in
Al/air electric vehicles (EVs) can be 15% (present stage) or 20% (projected),
comparable to that of internal combustion engine vehicles (ICEs) (13%). The
design battery energy density is 1300 Wh/kg (present) or 2000 Wh/kg
(projected). The cost of battery system chosen to evaluate is US$ 30/kW
(present) or US$ 29/kW (projected). Al/air EVs life-cycle analysis was
conducted and compared to lead/acid and nickel metal hydride (NiMH) EVs. Only
the Al/air EVs can be projected to have a travel range comparable to ICEs.
From this analysis, Al/air EVs are the most promising candidates compared to
ICEs in terms of travel range, purchase price, fuel cost, and life-cycle
cost._

Interestingly, Al batteries are missing from the MIT battery primer [0].

[0]
[http://web.mit.edu/2.009/www/resources/mediaAndArticles/batt...](http://web.mit.edu/2.009/www/resources/mediaAndArticles/batteriesPrimer.pdf)

~~~
foota
I think there's a pretty big difference between an aluminum air battery and
this.

------
pvaldes
They will need a way to cope with: sand grains, lime, phytoplancton,
gelatinous zooplancton, marine snow, sharks atracted by electric fields...
will need a microporous filter and a way to force the saltwater into the
device.

The problem with this concept is that this batteries could fail suddenly. Will
the oceanographers want to use it and take the risk? Even a small cube full of
Salinity and temperature sensors etc, can be valued in several millions.

A way to solve it could be to design a saltwater circuit totally closed and
autonomous. Like a gas deposit. Could even act as a shield for the machine. A
hole on this deposit and water entering on it? no harm done. Could be even an
automatic activation method for several types of rescue systems (Water
entering in the machine/ship after a crash, seawater-batteries activating
automatically)

------
gene-h
I recently saw a presentation by some college students that investigated the
feasibility of running ocean gliders on nuclear power. The proposal was to use
a nice sized chunk of strontium 90 for a radioisotopic thermal generator. This
would provide 45 watts electrical power for about 10 years.

The interesting part was not the technical feasibility, but how they were
going to make a case to the NRC to make such a use of radioisotopes legal.
Apparently there is a precedent for this, some scientific ice monitoring
equipment has used strontium 90 RTGs.

------
sgt
Perhaps this is something Liquid Robotics should (or already are) looking
into. That's the company James Gosling works for and they're doing fascinating
stuff with ocean robots.

[https://www.liquid-robotics.com/](https://www.liquid-robotics.com/)

------
algirau
I don't see any performance metrics.

~~~
ramzyo
My thoughts exactly. Tough to make any sort of evaluation of this technology
when the article doesn't provide any performance data or discuss the tradeoffs
of this solution (first thing that comes to mind is how heavy are these
batteries?)

------
nephrite
I really don't like that the hydrogen made in process is considered waste and
is escaping. We sure have a lot of water on planet but if the technology will
become mainstream and we will just throw the hydrogen away it will become a
huge problem.

~~~
simias
It seems like we're a very long way away from it being a practical problem.
And if it ever becomes an issue it doesn't sound like it will be very hard to
overcome. After all burning this hydrogen would release even more energy and
some water, although it would require a source of oxygen.

If anything I'd be more worried about the large scale effects of massive
amounts of aluminum hydroxide being released in the environment.

~~~
nephrite
At least aluminum hydroxide is solid, so it's easy to collect. Hydrogen is gas
though.

~~~
ema
Hydrogen in low concentrations isn't dangerous and it's gonna be slowly bonded
into water again whenever there is a flame or lightning strike.

~~~
Retric
Sunlight is also important for these reactions. There is quite a bit of ozone
which combines with hydrogen to become oxygen + water.

