There was a time, not so long ago, when computers were so large that they took up entire rooms. Today, some processing units can be as small as a few grains of dust.
Even next to a grain of rice, those micrometer-sized chip stacks seem infinitesimal.
Shrinking computer batteries to fit this size, however, has proven more difficult.
With little room for storage, smaller computers must rely on ultrasonic or photovoltaic cells to continuously recharge the microbatteries with energy from vibrations or sunlight. This has its drawbacks, as the computer will not work without a constant power supply or in dark places like the human body.
Some scientists in Europe therefore propose an alternative structure: a microbattery based on folding thin micro-layers like origami.
The battery is only a prototype for now, but preliminary results are encouraging.
“There is a desperate need to develop high-performance batteries for the millimeter and submillimeter size regime, as such energy storage systems would facilitate the development of truly autonomous microsystems,” the authors write.
Full-size computer batteries are typically based on “wet chemistry,” which means that electrically conductive metal sheets are placed in contact with liquid electrolytes to create energy flow.
Chip-based batteries of a certain size, however, cannot handle liquid electrolytes.
So the inventors of this new microbattery pressed a solid electrolyte between two microchips that are painted with a super-thin film of electrodes, one positive, one negative.
This solid electrolyte, however, is not as effective as using a liquid electrolyte, where folding comes into play.
By rolling a flat battery stack into a “Swiss roll cylinder,” scientists can squeeze much more surface area into a small space. That’s actually how the cylindrical cells in Tesla’s electric cars work.
At the scale of a cubic millimeter, it is extremely difficult to roll thin, brittle materials into this type of shape via external pressure.
Fortunately, there is another way to bend the material on its own, and it’s called “micro-origami.”
The technique works like a roller blind. As the thin material is pulled down, you can let go of that mechanical tension and it will soar and roll into a cylinder.
On a chip, the researchers were able to achieve this movement by attaching one side of the thin material to create, essentially, the bar of a blind.
Ultimately, the team was able to roll a prototype microbattery into an area of just 0.04 square millimeters, offering eight times the capacity of what a similar-sized flat battery could achieve.
The authors say the cylinder resembles the standard Swiss roll structure used in larger batteries, including at least two collector layers, a cathode film, an anode film and an electrolyte film all wound together.
Not only is the design rechargeable, but the researchers say the battery as it is could power the smallest computers we have for about 10 hours. And there’s still work to be done.