What battery chemistry is suitable for a "time capsule" applicaton?

Question

What battery chemistry would be most suitable for an application where the cells are expected to sit a very long time, say 100 years, disconnected, with minimal self discharge?

Assume the storage temperature would be something on the order of outdoor extremes experienced in inhabited places on Earth, say -50°C to 50°C or so.

Assume the operating temperature range would be narrower, say 0°C to 30°C or so.

It need not be a chemistry currently available in any commercial products. Assume environmental concerns can be overcome.

Assume the current demands are relatively low, for a small electronic data processing load and that physical space can be found to make a battery of sufficient capacity.

Assume that a hard switch (not a semiconductor) will disconnect the battery from the load.

It doesn't have to be a voltaic cell necessarily, just a self-contained means to store or generate electric energy. It must not rely on external sources of energy like sun, wind, water, or physical effort (like cranking a dynamo) which might not be available when the system is finally turned on.

To clarify the intent, this would be for a "time capsule" type use where it's expected to be sealed into construction, but must be able to power up in the future with no expectation of available external power.

Answer 1

A gravity-battery might be designed to drop a weight, generating energy, when the time-capsule's opened.

A gravity battery is a type of electricity storage device that stores gravitational energy, the energy stored in an object resulting from a change in height due to gravity, also called potential energy. A gravity battery works by using excess energy from the grid to raise a mass to generate gravitational potential energy, which is then dropped to convert potential energy into electricity through an electric generator. Energy generated from a gravity battery is a form of sustainable energy. One form of a gravity battery is one that lowers a mass, such as a block of concrete, to generate electricity. The most common gravity battery is used in pumped-storage hydroelectricity, where water is pumped to higher elevations to store energy and released through water turbines to generate electricity.

—"Gravity battery", Wikipedia [links and references omitted]

Answer 2

The longest operating battery: https://en.wikipedia.org/wiki/Oxford_Electric_Bell

No exotic chemistry required, but it's very effectively insulated so as to prevent self-discharge.

Answer 3

Industrial Zinc-air batteries have a very long shelf life. They need to be activated (pull-tab) and require an oxygen environment which may invalidate this battery for your needs.

Answer 4

A nuclear-diamond battery is probably the best choice, they could last for 100's of years.

In 2018, researchers from the Moscow Institute of Physics and Technology (MIPT), the Technological Institute for Superhard and Novel Carbon Materials (TISNCM), and the National University of Science and Technology (MISIS) announced a prototype using 2-micron thick layers of 63Ni foil sandwiched between 200 10-micron diamond converters. It produced a power output of about 1 μW at for power density of 10 μW/cm3. At those values, its energy density would be approximately 3.3 Wh/g over its 100 year half-life, about 10 times that of conventional electrochemical batteries.[6] This research was published in April of 2018 in the Diamond and Related Materials journal.[7]

Source: https://en.wikipedia.org/wiki/Diamond_battery

Answer 5

Thermal batteries (an unfortunate name because they are not hot until activated) are used in military applications such as missiles. They are activated by a built-in pyrotechnic charge and have an advertised shelf life of 50 years. It's not hard to imagine a greatly extended shelf life through improved sealing.

They typically produce a great deal of electric power for a relatively short amount of time, such as the amount needed to steer a missile using strong servo motors. Since you need lower currents, you could combine a thermal battery that runs for a few minutes together with a supercapacitor for long duration, low power use.

To activate, you could pull a pin that allows a spring-loaded hammer to strike an internal primer. Within milliseconds, great gobs of power would be flowing to charge your supercapacitor.

Answer 6

Let's assume we're talking an Earth-bound solution. If the location has a consistent ambient thermal gradient available, and your power needs are low, perhaps a thermopile combined with some energy-harvesting + storage setup could work. This is kind of like using a radioisotope thermal generator (RTG) as used in spacecraft, but without the hazardous material risk (not to mention the government red tape in obtaining such a device.)

An idea that could provide round-the-clock power:

• Day harvesting - lensed solar to heat the thermopile hot side, cool side in the ground
• Night harvesting - ground-source heat to the hot side, cool side in air

Challenge: thermopiles are very inefficient (about 7.5%.) But with a large enough pile and big enough gradient you can get useable power. Piles sold for use with woodstoves generate hundreds of W. More about those here: https://www.tegmart.com/

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Now, if the requirement is that the device have a means to power itself when opened, but otherwise isn't powered on, then why not solar? With the cells protected from the elements until the capsule is opened, the cells will not age like they do when exposed to light and heat.

Likewise, a wind or water turbine, hand crank, or some other electromechanical generator could generate power. There's kind of a neat wind approach that uses a single, flexible blade: https://www.bridgestone.com/bwsc/stories/article/2019/11/13-2.html

Finally, I think power supplies that use a triggered chemical reaction are problematic for long term, because of shelf life. That said, an 'idiot-simple' solution could be a lead-acid battery that has its electrolyte separate. Open the capsule, pour in the electrolyte and you have a pretty big battery at about 50% state-of-charge.

Answer 7

I would try going back to basics and supply the separate parts to make a Voltaic pile: copper and zinc plates, cardboard separators and salty brine along with instructions. You could scale the electrode area and stack height to get the required current and voltage for your load.

Answer 8

Thinking out of the box here: does the energy really have to be inside of the "battery"?

Maybe include a solar panel hooked up to the device, along with instructions for the future users that they need to place it in sunlight?

Or... if you expect there not to be any sun anymore by the time they discover the time capsule: a dynamo with hand crank, along with instructions that they should spin the crank?

Answer 9

Not exactly a "battery" but for the application, a fuel cell might work well. Use spring energy to puncture sealed tanks of hydrogen and oxygen, and a moment later a second mechanical device creates a spark, and your fuel cell roars to life. Once it's operating & producing power, an electronic controller could throttle the feeds to regulate the output.