Salt water batteries hold powerful advantages in applications where size and weight are less important factors

By Gary Elinoff, contributing writer

Salt water batteries are not
likely to ever substitute for lithium-ion batteries for use in portable
devices. This is because they can’t hold as much charge in the same package
size and weight, or putting it another way, they are less energy dense. But,
they hold some powerful advantages in applications where size and weight are
less important factors. 

Basic batteries

The building blocks of a battery
are the cathode and anode, and an electrolyte that allows the cathode and anode
to exchange ions in one direction as they deliver electricity, or in the other
direction as it is being recharged. 

For a lithium-ion battery, the
anode, or the negative terminal can be graphite, while the cathode, or positive
terminal might be constructed of a lithium metal oxide. The electrolyte allows
lithium ions (hence the name) to flow from cathode to anode during charging as
illustrated, or in the opposite direction when the battery is delivering,
rather than storing energy.

The separator is porous to the
traveling ions, but must prevent the anode or cathode from touching, or
disaster results. The electrolyte is generally flammable. 

All in all, as recent news events
have proven, the lithium ion battery is a dangerous proposition. We’ve taken a
walk on the wild side, now let’s relax and move over to the mild side. 

Salt water batteries 

The electrolyte for a saltwater
battery is nothing more then that, saltwater, hence the device’s name. The
anode can be carbon, and the cathode can be a material such as manganese oxide.
In this illustration, the anode is zinc.




The essence of a salt water battery. Image source: SPIE.

With no hazardous materials in
their construction, unlike lithium ion batteries they are non-toxic and they
can’t explode. Because of this, there is no need for the complex and
troublesome electronic circuitry that every lithium-ion battery needs to insure
that they charge and discharge only within safe parameters. In addition, unlike
their lithium-based cousins, salt water batteries can be more deeply discharged
(drained of electrical energy) with no damage to the battery.


Commercialization of saltwater batteries


There is, so far, one major
manufacturer of saltwater batteries, and it has run into some non-technological
problems, so at least temporarily, they have suspended operations. The technology
itself has been well received, but in the battery business, a producer has to
get big fast or go home. Smart money expects another concern with deeper
pockets, most likely a provider of solar energy systems, to pick up the ball
and run with it.


It’s especially worth noting that
many economists predict a looming worldwide shortage of lithium itself due to
the electric car boon. Salt water batteries are an emerging technology, and
many different forms are under development, but one thing they all share is a
very prosaic bill of materials – there will be no shortages of carbon,
manganese oxide, water or salt.


Indeed, salt water batteries are
so safe, simplified versions make great projects for kids. Watch this little guy
light it up.

Storing renewable energy


The biggest disadvantage of all
forms of salt water batteries is that to store a given amount of electricity,
they are bulkier and heavier that other commercially available batteries. As it
turns out, there is one huge potential use for these devices where that will be
no issue at all – smoothing out power from large-scale renewable energy
generation plants.


The sun doesn’t always shine, and
the wind doesn’t always blow. For this reason, the electrical output of
renewable plants is, by nature intermittent. Salt water batteries can be
charged by that excess energy generated during times of high output, and then
release that stored power to the grid when it is needed.


Since the sun shines as brightly
and the wind blows as intensely in remote areas as they do anywhere else,
renewable energy plants are most often located in remote areas where land is
cheap. In such locations, the added footprint of a less energy-dense battery
system is not an issue, making salt water batteries the ideal choice. The
electricity can be ferried to population centers via another just-emerging
technology – high voltage DC superconducting lines – but that’s a subject for
another blog.