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Ultra-Long-Life Battery
Jamais Cascio, 15 May 05

One of the problems with spreading environmental sensors far and wide is the need to power them. While most of these sensors are designed to use as little power as possible, few can be run solely on photovoltaics; batteries, therefore, are a necessary component. So what can provide the best power over an extended period?

It may be tritium. Tritium is an isotope of hydrogen and, yes, it's radioactive. But before you click the comment button, read on.

Tritium batteries work by absorbing beta-decay electrons in a silicon panel similar to traditional photovoltaics. The concept isn't new, but earlier designs were unable to capture a sufficient number of electrons to provide a significant amount of power. The new design, figured out by researchers from the University of Rochester, the University of Toronto, Rochester Institute of Technology and BetaBatt, Inc. of Houston, Texas, uses a 3D porous silicon matrix which gives it vastly increased surface area. Tritium batteries can last for at least 12 years (the half-life of tritium) of continuous use up to over a century, depending upon battery design -- a significant improvement over traditional chemical batteries.

But what about the safety?

There were a number of practical reasons for selecting tritium as the source of energy, says co-author Larry Gadeken of BetaBatt - particularly safety and containment.

"Tritium emits only low energy beta particles (electrons) that can be shielded by very thin materials, such as a sheet of paper," says Gadeken. "The hermetically-sealed, metallic BetaBattery cases will encapsulate the entire radioactive energy source, just like a normal battery contains its chemical source so it cannot escape."

Even if the hermetic case were to be breached, adds Gadeken, the source material the team is developing will be a hard plastic that incorporates tritium into its chemical structure. Unlike a chemical paste, the plastic cannot not leak out or leach into the surrounding environment.

(The beta-decay electrons from tritium are incredibly weak; a layer of dead skin is sufficient to block their entry from external sources. Swallowing tritium poses marginally more risk, but even so, tritium is typically flushed from the system within a couple of days or weeks, and even large doses amount to at most a couple of years worth of natural background radiation -- or one round-trip transatlantic flight.)

There are undoubtedly some readers who will oppose this, no matter how limited the actual danger; that's understandable. But in this case, the potential risk -- even in the worst-case scenario, consumption of material from a breached container -- is so slight, and the potential rewards -- long-life sensor and monitoring equipment -- so significant, it seems a highly worthwhile research path. I anticipate an interesting discussion in the comments.

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Comments

One just has to do a cost benefit analysis. It would seem that the batteries have a far greater potential to benefit than to harm.

If one toes the hardline one things like radiation emission, he might as well ditch his cell phone (which I have done! but anyway).


Posted by: livingfossil on 15 May 05

Polluting the world with so-called "trace" amounts of pollutants is nothing to ignore. Just because it's safe for humans in an immediate sense of physical threat doesn't mean that it's *safe*, nor worth humanity's while to deploy and allow to be dispersed. The delicacies involved in normal reproduction of most forms of biological life are only just beginning to register on us to the point where it's becoming understood that the pill and so-called "trace" amounts of pharmeceuticals in tap water, for example, are quite enough to radically throw out of whack some of the most basic life processes.


Posted by: dynamist on 15 May 05

EnOcean (http://www.enocean.com/index_en.html) is exploring another solution. They develop sensors that "harvest energy" from the environment. No batteries. No fuel.

Neat stuff, if you ask me.


Posted by: Ken Dyck on 17 May 05

This is great. I for one am fed up of battery technologies not advancing at the same (or similar) rate as other technology so this is a quantum leap forward in my book. And hopefully it will be a quantum leap forward in my iBook too ;)

As an aside, tritium used to be used for the roman numerals on old style watch faces as it glows in the dark. Apparently, there were many instances of the women who painted the numerals on by hand developing throat and/or mouch cancer after working for years and years in this business. This was because they frequently licked the paintbrush to get a very fine point, dipped it in the tritium and then repeated... So, ingesting tritium is bad. Which is fairly obvious. No, no licking of these new batteries, ok? especially not hundreds and thousands of times a day!


Posted by: Matt on 17 May 05

Matt's comment is incorrect where he states that tritium used to be used for painting clockfaces. In fact the substance used was radium. However he is correct that workers licked the paintbrushes to get fine points and then developed health consequences.

Tritium in its gaseous form was used in glow-in-the-dark telephone dials by the UK's General Post Office (GPO, prior to British Telecom). The Trimphone, or "Tele. No. 722" (not related to the Western Electric "Trimline" in the US) has become a 20th century classic and examples are still widely available (I have one, it still glows).

GPO's internal technical documents called for certain precautions such as limiting the number of Trimphones or replacement dials carried in a GPO vehicle, special handling in the event of damage, etc. However, thousands of these phones were made and used, very often installed on bedside tables. There doesn't seem to have been a history of health problems associated with them, either on the part of users, technicians, or manufacturers.

That being said, there is still good reason to limit the use of radioactive materials in consumer devices. GPO, like the old Bell System, had cradle-to-grave responsibility for their equipment. Phones were repaired on site or reconditioned by manufacturers, rather than being tossed into the trash. The dials with the pleasant blue glow did not end up contaminating landfills.

If tritium batteries are produced, a reasonable deposit should be charged, and then refunded when the batteries are returned to the manufacturer for proper disposal. This at least will keep most of them out of the municipal waste stream.

Aside from that, it may be preferable to investigate the use of Toshiba's new rapid-charging battery for applications such as remote environmental monitoring stations. These batteries could be recharged by small wind generators or PV panels, admittedly at higher cost, but without the need for such close control.

Here I should mention that I am not given to fears about radioactivity as such. In fact I agree with those in the green community who have concluded -often with reluctance to speak publicly about this- that the new designs for nuclear fission reactors offer a safer alternative to coal for meeting energy needs in an era where petroleum supplies are declining. Even with massive deployment of sustainable energy sources and massive increases in efficiency standards, any reasonable assessment shows we still need to expand our nuclear capacity. We can and should be discussing the new reactor designs, to arrive at a green consensus about their relative merits.


Posted by: George on 17 May 05

I thought watch dial painting cancer problems happened with radium, which is much more potent than tritium. One source here

http://elginwatches.org/help/luminous_dials.html


Posted by: Adam Burke on 17 May 05

there are tritium sights on pistols


Posted by: mlhm5 on 18 May 05



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